jsonpb: Format and parse the WKTs in wrappers.proto.

Per the spec, they are meant to use the same representation
in JSON as the wrapped primitive type. Fortunately for us,
that is trivial to implement.
diff --git a/jsonpb/jsonpb.go b/jsonpb/jsonpb.go
index f4523f5..d1f6f28 100644
--- a/jsonpb/jsonpb.go
+++ b/jsonpb/jsonpb.go
@@ -107,6 +107,12 @@
 	}
 	if wkt, ok := v.(wkt); ok {
 		switch wkt.XXX_WellKnownType() {
+		case "DoubleValue", "FloatValue", "Int64Value", "UInt64Value",
+			"Int32Value", "UInt32Value", "BoolValue", "StringValue", "BytesValue":
+			// "Wrappers use the same representation in JSON
+			//  as the wrapped primitive type, ..."
+			sprop := proto.GetProperties(s.Type())
+			return m.marshalValue(out, sprop.Prop[0], s.Field(0), indent)
 		case "Duration":
 			// "Generated output always contains 3, 6, or 9 fractional digits,
 			//  depending on required precision."
@@ -427,6 +433,13 @@
 	}
 	if wkt, ok := target.Addr().Interface().(wkt); ok {
 		switch wkt.XXX_WellKnownType() {
+		case "DoubleValue", "FloatValue", "Int64Value", "UInt64Value",
+			"Int32Value", "UInt32Value", "BoolValue", "StringValue", "BytesValue":
+			// "Wrappers use the same representation in JSON
+			//  as the wrapped primitive type, except that null is allowed."
+			// encoding/json will turn JSON `null` into Go `nil`,
+			// so we don't have to do any extra work.
+			return unmarshalValue(target.Field(0), inputValue)
 		case "Duration":
 			unq, err := strconv.Unquote(string(inputValue))
 			if err != nil {
diff --git a/jsonpb/jsonpb_test.go b/jsonpb/jsonpb_test.go
index f5612b9..a970063 100644
--- a/jsonpb/jsonpb_test.go
+++ b/jsonpb/jsonpb_test.go
@@ -41,6 +41,7 @@
 	proto3pb "github.com/golang/protobuf/proto/proto3_proto"
 	durpb "github.com/golang/protobuf/ptypes/duration"
 	tspb "github.com/golang/protobuf/ptypes/timestamp"
+	wpb "github.com/golang/protobuf/ptypes/wrappers"
 )
 
 var (
@@ -321,6 +322,16 @@
 
 	{"Duration", marshaler, &pb.KnownTypes{Dur: &durpb.Duration{Seconds: 3}}, `{"dur":"3.000s"}`},
 	{"Timestamp", marshaler, &pb.KnownTypes{Ts: &tspb.Timestamp{Seconds: 14e8, Nanos: 21e6}}, `{"ts":"2014-05-13T16:53:20.021Z"}`},
+
+	{"DoubleValue", marshaler, &pb.KnownTypes{Dbl: &wpb.DoubleValue{Value: 1.2}}, `{"dbl":1.2}`},
+	{"FloatValue", marshaler, &pb.KnownTypes{Flt: &wpb.FloatValue{Value: 1.2}}, `{"flt":1.2}`},
+	{"Int64Value", marshaler, &pb.KnownTypes{I64: &wpb.Int64Value{Value: -3}}, `{"i64":"-3"}`},
+	{"UInt64Value", marshaler, &pb.KnownTypes{U64: &wpb.UInt64Value{Value: 3}}, `{"u64":"3"}`},
+	{"Int32Value", marshaler, &pb.KnownTypes{I32: &wpb.Int32Value{Value: -4}}, `{"i32":-4}`},
+	{"UInt32Value", marshaler, &pb.KnownTypes{U32: &wpb.UInt32Value{Value: 4}}, `{"u32":4}`},
+	{"BoolValue", marshaler, &pb.KnownTypes{Bool: &wpb.BoolValue{Value: true}}, `{"bool":true}`},
+	{"StringValue", marshaler, &pb.KnownTypes{Str: &wpb.StringValue{Value: "plush"}}, `{"str":"plush"}`},
+	{"BytesValue", marshaler, &pb.KnownTypes{Bytes: &wpb.BytesValue{Value: []byte("wow")}}, `{"bytes":"d293"}`},
 }
 
 func TestMarshaling(t *testing.T) {
@@ -363,6 +374,18 @@
 
 	{"Duration", `{"dur":"3.000s"}`, &pb.KnownTypes{Dur: &durpb.Duration{Seconds: 3}}},
 	{"Timestamp", `{"ts":"2014-05-13T16:53:20.021Z"}`, &pb.KnownTypes{Ts: &tspb.Timestamp{Seconds: 14e8, Nanos: 21e6}}},
+
+	{"DoubleValue", `{"dbl":1.2}`, &pb.KnownTypes{Dbl: &wpb.DoubleValue{Value: 1.2}}},
+	{"FloatValue", `{"flt":1.2}`, &pb.KnownTypes{Flt: &wpb.FloatValue{Value: 1.2}}},
+	{"Int64Value", `{"i64":"-3"}`, &pb.KnownTypes{I64: &wpb.Int64Value{Value: -3}}},
+	{"UInt64Value", `{"u64":"3"}`, &pb.KnownTypes{U64: &wpb.UInt64Value{Value: 3}}},
+	{"Int32Value", `{"i32":-4}`, &pb.KnownTypes{I32: &wpb.Int32Value{Value: -4}}},
+	{"UInt32Value", `{"u32":4}`, &pb.KnownTypes{U32: &wpb.UInt32Value{Value: 4}}},
+	{"BoolValue", `{"bool":true}`, &pb.KnownTypes{Bool: &wpb.BoolValue{Value: true}}},
+	{"StringValue", `{"str":"plush"}`, &pb.KnownTypes{Str: &wpb.StringValue{Value: "plush"}}},
+	{"BytesValue", `{"bytes":"d293"}`, &pb.KnownTypes{Bytes: &wpb.BytesValue{Value: []byte("wow")}}},
+	// `null` is also a permissible value. Let's just test one.
+	{"null DoubleValue", `{"dbl":null}`, &pb.KnownTypes{Dbl: &wpb.DoubleValue{}}},
 }
 
 func TestUnmarshaling(t *testing.T) {
diff --git a/jsonpb/jsonpb_test_proto/Makefile b/jsonpb/jsonpb_test_proto/Makefile
index d16e916..d6e9768 100644
--- a/jsonpb/jsonpb_test_proto/Makefile
+++ b/jsonpb/jsonpb_test_proto/Makefile
@@ -30,4 +30,4 @@
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 regenerate:
-	protoc --go_out=Mgoogle/protobuf/duration.proto=github.com/golang/protobuf/ptypes/duration,Mgoogle/protobuf/timestamp.proto=github.com/golang/protobuf/ptypes/timestamp:. *.proto
+	protoc --go_out=Mgoogle/protobuf/duration.proto=github.com/golang/protobuf/ptypes/duration,Mgoogle/protobuf/timestamp.proto=github.com/golang/protobuf/ptypes/timestamp,Mgoogle/protobuf/wrappers.proto=github.com/golang/protobuf/ptypes/wrappers:. *.proto
diff --git a/jsonpb/jsonpb_test_proto/test_objects.pb.go b/jsonpb/jsonpb_test_proto/test_objects.pb.go
index cf6f0e3..de58e89 100644
--- a/jsonpb/jsonpb_test_proto/test_objects.pb.go
+++ b/jsonpb/jsonpb_test_proto/test_objects.pb.go
@@ -9,6 +9,7 @@
 import math "math"
 import google_protobuf "github.com/golang/protobuf/ptypes/duration"
 import google_protobuf1 "github.com/golang/protobuf/ptypes/timestamp"
+import google_protobuf2 "github.com/golang/protobuf/ptypes/wrappers"
 
 // Reference imports to suppress errors if they are not otherwise used.
 var _ = proto.Marshal
@@ -517,9 +518,18 @@
 }
 
 type KnownTypes struct {
-	Dur              *google_protobuf.Duration   `protobuf:"bytes,1,opt,name=dur" json:"dur,omitempty"`
-	Ts               *google_protobuf1.Timestamp `protobuf:"bytes,2,opt,name=ts" json:"ts,omitempty"`
-	XXX_unrecognized []byte                      `json:"-"`
+	Dur              *google_protobuf.Duration     `protobuf:"bytes,1,opt,name=dur" json:"dur,omitempty"`
+	Ts               *google_protobuf1.Timestamp   `protobuf:"bytes,2,opt,name=ts" json:"ts,omitempty"`
+	Dbl              *google_protobuf2.DoubleValue `protobuf:"bytes,3,opt,name=dbl" json:"dbl,omitempty"`
+	Flt              *google_protobuf2.FloatValue  `protobuf:"bytes,4,opt,name=flt" json:"flt,omitempty"`
+	I64              *google_protobuf2.Int64Value  `protobuf:"bytes,5,opt,name=i64" json:"i64,omitempty"`
+	U64              *google_protobuf2.UInt64Value `protobuf:"bytes,6,opt,name=u64" json:"u64,omitempty"`
+	I32              *google_protobuf2.Int32Value  `protobuf:"bytes,7,opt,name=i32" json:"i32,omitempty"`
+	U32              *google_protobuf2.UInt32Value `protobuf:"bytes,8,opt,name=u32" json:"u32,omitempty"`
+	Bool             *google_protobuf2.BoolValue   `protobuf:"bytes,9,opt,name=bool" json:"bool,omitempty"`
+	Str              *google_protobuf2.StringValue `protobuf:"bytes,10,opt,name=str" json:"str,omitempty"`
+	Bytes            *google_protobuf2.BytesValue  `protobuf:"bytes,11,opt,name=bytes" json:"bytes,omitempty"`
+	XXX_unrecognized []byte                        `json:"-"`
 }
 
 func (m *KnownTypes) Reset()                    { *m = KnownTypes{} }
@@ -541,6 +551,69 @@
 	return nil
 }
 
+func (m *KnownTypes) GetDbl() *google_protobuf2.DoubleValue {
+	if m != nil {
+		return m.Dbl
+	}
+	return nil
+}
+
+func (m *KnownTypes) GetFlt() *google_protobuf2.FloatValue {
+	if m != nil {
+		return m.Flt
+	}
+	return nil
+}
+
+func (m *KnownTypes) GetI64() *google_protobuf2.Int64Value {
+	if m != nil {
+		return m.I64
+	}
+	return nil
+}
+
+func (m *KnownTypes) GetU64() *google_protobuf2.UInt64Value {
+	if m != nil {
+		return m.U64
+	}
+	return nil
+}
+
+func (m *KnownTypes) GetI32() *google_protobuf2.Int32Value {
+	if m != nil {
+		return m.I32
+	}
+	return nil
+}
+
+func (m *KnownTypes) GetU32() *google_protobuf2.UInt32Value {
+	if m != nil {
+		return m.U32
+	}
+	return nil
+}
+
+func (m *KnownTypes) GetBool() *google_protobuf2.BoolValue {
+	if m != nil {
+		return m.Bool
+	}
+	return nil
+}
+
+func (m *KnownTypes) GetStr() *google_protobuf2.StringValue {
+	if m != nil {
+		return m.Str
+	}
+	return nil
+}
+
+func (m *KnownTypes) GetBytes() *google_protobuf2.BytesValue {
+	if m != nil {
+		return m.Bytes
+	}
+	return nil
+}
+
 var E_Name = &proto.ExtensionDesc{
 	ExtendedType:  (*Real)(nil),
 	ExtensionType: (*string)(nil),
@@ -564,56 +637,65 @@
 }
 
 var fileDescriptor1 = []byte{
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+	// 947 bytes of a gzipped FileDescriptorProto
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+	0xaa, 0x3c, 0x94, 0x44, 0x23, 0x61, 0x95, 0xde, 0xc4, 0x79, 0xa6, 0xe2, 0x3a, 0xf4, 0x51, 0x71,
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+	0x1c, 0xe9, 0x65, 0x13, 0x57, 0x43, 0x5a, 0x2c, 0x43, 0x8e, 0x52, 0x40, 0x71, 0x7a, 0x69, 0xe2,
+	0x16, 0x6b, 0x3c, 0x91, 0x70, 0x88, 0xca, 0x75, 0x8c, 0x3b, 0xa4, 0xd5, 0xe4, 0x1f, 0x87, 0x7b,
+	0x32, 0x29, 0x93, 0xb8, 0xae, 0x08, 0x14, 0xb4, 0xa0, 0x18, 0x81, 0x82, 0x16, 0x14, 0x74, 0xa0,
+	0x18, 0x81, 0x82, 0x0e, 0x14, 0x74, 0xa0, 0x18, 0x81, 0x82, 0x0e, 0x14, 0x58, 0x50, 0x8c, 0x40,
+	0x81, 0x05, 0x05, 0x16, 0x14, 0x23, 0x50, 0x60, 0x41, 0x81, 0x05, 0xc5, 0x08, 0x14, 0x9c, 0x6c,
+	0x54, 0x75, 0xa0, 0x18, 0x81, 0x02, 0x0b, 0x0a, 0x3a, 0x50, 0x8c, 0x40, 0x41, 0x07, 0x0a, 0x2c,
+	0x28, 0x46, 0xa0, 0xc0, 0x82, 0x02, 0x0b, 0x8a, 0x11, 0x28, 0xb0, 0xa0, 0xa0, 0x03, 0xc5, 0x08,
+	0x14, 0x18, 0x50, 0xff, 0x62, 0x43, 0x3d, 0x4f, 0xcf, 0x96, 0x49, 0x2d, 0xee, 0x72, 0xf7, 0x85,
+	0xca, 0x14, 0xe8, 0x7e, 0xda, 0x9f, 0x1e, 0x44, 0xa6, 0xa9, 0x23, 0x23, 0x47, 0x8f, 0x49, 0x93,
+	0xc6, 0x22, 0x3e, 0xa3, 0x3c, 0xe3, 0x26, 0x78, 0xbb, 0xdc, 0x03, 0xd0, 0xff, 0xc5, 0x1d, 0x3e,
+	0xa8, 0x74, 0xd7, 0xea, 0x03, 0x1c, 0x4e, 0xf7, 0x5b, 0xb7, 0xe9, 0x65, 0xd9, 0xa8, 0xe2, 0x63,
+	0x03, 0x44, 0x3b, 0x69, 0x9f, 0xdb, 0x4e, 0x02, 0xd4, 0x58, 0x3d, 0x30, 0x07, 0x1c, 0x1e, 0xe8,
+	0xcc, 0x37, 0x5a, 0x67, 0x73, 0xee, 0xb2, 0xd5, 0xc5, 0xa7, 0x3c, 0x80, 0x79, 0x6b, 0xbe, 0xa1,
+	0x63, 0xb7, 0xcc, 0x3e, 0x34, 0xbf, 0x26, 0x1f, 0x72, 0xd7, 0x6c, 0xda, 0xe3, 0x4c, 0xce, 0x8e,
+	0x46, 0xd7, 0x44, 0xc0, 0xdd, 0x6f, 0xe5, 0x6c, 0xf6, 0x74, 0xd4, 0x13, 0x3e, 0xef, 0x1f, 0xfe,
+	0x70, 0x3a, 0x1b, 0x39, 0x93, 0x3f, 0x1d, 0xde, 0x3f, 0x8e, 0xcb, 0x4a, 0x7c, 0xc9, 0x87, 0xb9,
+	0x69, 0x17, 0x62, 0xaf, 0x7b, 0x6c, 0x38, 0x7d, 0xa7, 0xcd, 0x27, 0x4b, 0x74, 0xac, 0xfb, 0x07,
+	0x8f, 0x62, 0x56, 0xd4, 0xb0, 0x96, 0x41, 0xde, 0xae, 0xc5, 0xd7, 0x7c, 0x2f, 0xd7, 0xbd, 0xd9,
+	0x3e, 0xb5, 0xa3, 0xcb, 0xdf, 0xbd, 0x5c, 0x4e, 0xfd, 0x6a, 0x1e, 0xdb, 0x04, 0x0c, 0x73, 0x7b,
+	0x65, 0xfc, 0x15, 0xdf, 0xbf, 0x9c, 0x2f, 0x46, 0x9c, 0xfd, 0x92, 0xac, 0xf5, 0x31, 0x32, 0x49,
+	0x3f, 0xc5, 0x01, 0x77, 0x7f, 0x8d, 0xb3, 0x55, 0xa2, 0x47, 0x42, 0x20, 0xcd, 0xe2, 0x91, 0xf3,
+	0x45, 0x6f, 0xfc, 0x94, 0x8f, 0xae, 0xc6, 0x6f, 0xd6, 0xfb, 0xa6, 0xfe, 0x83, 0xcd, 0xfa, 0xed,
+	0x43, 0xb1, 0x79, 0x93, 0x27, 0xfc, 0xfa, 0x71, 0xb5, 0x7c, 0x9e, 0xd6, 0x3f, 0xff, 0x58, 0x24,
+	0xea, 0x5c, 0xbc, 0xc5, 0xdd, 0x3a, 0xad, 0xf1, 0xc1, 0x28, 0x2d, 0xf8, 0xee, 0x9a, 0x34, 0x4b,
+	0x11, 0x62, 0x47, 0xc4, 0x59, 0x0c, 0x6b, 0x1d, 0xc9, 0x50, 0x68, 0xd6, 0x87, 0x1e, 0x77, 0x57,
+	0x05, 0x8e, 0xcc, 0xc9, 0x1d, 0xde, 0x97, 0x49, 0x9c, 0xd9, 0xcd, 0xf7, 0xf4, 0x5c, 0x30, 0x8b,
+	0xbb, 0xbe, 0x7f, 0x36, 0xfa, 0x03, 0xff, 0x9c, 0xc9, 0x05, 0xf7, 0x1e, 0x2b, 0xda, 0xc7, 0x2b,
+	0x71, 0x8b, 0x07, 0x69, 0x1e, 0x2f, 0xd3, 0x82, 0x82, 0x8d, 0xdd, 0x5e, 0xb0, 0x25, 0xd3, 0x23,
+	0xbe, 0x0f, 0x18, 0x3d, 0x4f, 0x5e, 0xd5, 0x49, 0x51, 0xe1, 0xcd, 0xc4, 0x75, 0xdb, 0x10, 0x71,
+	0x16, 0xfe, 0x76, 0xb9, 0xa3, 0x9a, 0x78, 0xb9, 0x47, 0x45, 0xb3, 0xb6, 0x66, 0xf2, 0x57, 0x9f,
+	0xf3, 0xef, 0x0b, 0x75, 0x51, 0x3c, 0x5b, 0x97, 0x49, 0x25, 0x3e, 0xe1, 0x0c, 0xc7, 0xbd, 0xbe,
+	0xed, 0x70, 0x7a, 0x33, 0x32, 0x93, 0x3c, 0x6a, 0x27, 0x79, 0x74, 0xd4, 0x7c, 0x0a, 0x24, 0xb9,
+	0xf0, 0x65, 0x73, 0xb0, 0x19, 0x0d, 0xce, 0xf1, 0x96, 0xf7, 0x59, 0xfb, 0x59, 0x90, 0xe8, 0x12,
+	0x11, 0x06, 0x2f, 0x32, 0x3d, 0xb5, 0x87, 0xd3, 0x5b, 0xdb, 0xc1, 0xfa, 0xed, 0xff, 0x89, 0xa8,
+	0x48, 0x32, 0xe2, 0xcb, 0xc9, 0xce, 0xb3, 0x5a, 0xcf, 0x72, 0xea, 0xc4, 0xab, 0x7e, 0x3d, 0x47,
+	0x1a, 0x3b, 0xfa, 0xc8, 0x9e, 0x36, 0xf3, 0xfd, 0x75, 0x76, 0xdd, 0x5b, 0x8d, 0x1d, 0x7d, 0xb4,
+	0x9b, 0x15, 0xda, 0x07, 0x3b, 0x76, 0x73, 0xba, 0xe9, 0x47, 0xa3, 0x8e, 0xc7, 0xd1, 0xe7, 0xed,
+	0x8e, 0xbf, 0x3f, 0x6d, 0xe3, 0x71, 0x26, 0x52, 0x3c, 0xda, 0xfd, 0xff, 0x89, 0xef, 0xfc, 0x2b,
+	0xed, 0xef, 0xeb, 0xd9, 0x1e, 0xec, 0x40, 0x49, 0xcd, 0x6d, 0xec, 0xda, 0x47, 0xf9, 0xf4, 0x9a,
+	0xf2, 0x1d, 0xf9, 0x66, 0x5e, 0x36, 0xf9, 0x68, 0x14, 0x9f, 0x73, 0xd7, 0x7e, 0x60, 0x5e, 0xf7,
+	0x00, 0x7a, 0x8e, 0x9a, 0x02, 0xe3, 0x7c, 0x74, 0x9b, 0xf7, 0x8b, 0x38, 0x4f, 0xae, 0xf4, 0xd4,
+	0xef, 0xfa, 0xd5, 0xd3, 0xca, 0x7f, 0x01, 0x00, 0x00, 0xff, 0xff, 0xa1, 0xac, 0xb6, 0x4e, 0x44,
+	0x08, 0x00, 0x00,
 }
diff --git a/jsonpb/jsonpb_test_proto/test_objects.proto b/jsonpb/jsonpb_test_proto/test_objects.proto
index 8087f71..394c424 100644
--- a/jsonpb/jsonpb_test_proto/test_objects.proto
+++ b/jsonpb/jsonpb_test_proto/test_objects.proto
@@ -33,6 +33,7 @@
 
 import "google/protobuf/duration.proto";
 import "google/protobuf/timestamp.proto";
+import "google/protobuf/wrappers.proto";
 
 package jsonpb;
 
@@ -115,4 +116,14 @@
 message KnownTypes {
   optional google.protobuf.Duration dur = 1;
   optional google.protobuf.Timestamp ts = 2;
+
+  optional google.protobuf.DoubleValue dbl = 3;
+  optional google.protobuf.FloatValue flt = 4;
+  optional google.protobuf.Int64Value i64 = 5;
+  optional google.protobuf.UInt64Value u64 = 6;
+  optional google.protobuf.Int32Value i32 = 7;
+  optional google.protobuf.UInt32Value u32 = 8;
+  optional google.protobuf.BoolValue bool = 9;
+  optional google.protobuf.StringValue str = 10;
+  optional google.protobuf.BytesValue bytes = 11;
 }