[New go generator] Implement declaring unions.

mojom/generators/go/translator/translator.go

Index: mojom/generators/go/translator/translator.go
diff --git a/mojom/generators/go/translator/translator.go b/mojom/generators/go/translator/translator.go
index 1862fd45c515dcd9aa863d4b7eeda8b32e094ef1..7629754cf8e6758278270d0d31476fb08520cd28 100644
--- a/mojom/generators/go/translator/translator.go
+++ b/mojom/generators/go/translator/translator.go
@@ -41,6 +41,11 @@ func (t *translator) TranslateMojomFile(fileName string) (tmplFile *TmplFile) {
 		tmplFile.Structs[i] = t.translateMojomStruct(typeKey)
 	}
 
+	tmplFile.Unions = make([]*UnionTemplate, len(*file.DeclaredMojomObjects.Unions))
+	for i, typeKey := range *file.DeclaredMojomObjects.Unions {
+		tmplFile.Unions[i] = t.translateMojomUnion(typeKey)
+	}
+
 	tmplFile.Imports = []Import{
 		Import{PackagePath: "mojo/public/go/bindings", PackageName: "bindings"},
 		Import{PackagePath: "fmt", PackageName: "fmt"},
@@ -58,7 +63,7 @@ func (t *translator) translateMojomStruct(typeKey string) (m *StructTemplate) {
 	u := t.GetUserDefinedType(typeKey)
 	s, ok := u.Interface().(mojom_types.MojomStruct)
 	if !ok {
-		panic(fmt.Sprintf("%s is not a struct.", userDefinedTypeShortName(u)))
+		log.Panicf("%s is not a struct.", userDefinedTypeShortName(u))
 	}
 	m.Name = t.goTypeName(typeKey)
 	m.PrivateName = privateName(m.Name)
@@ -93,6 +98,32 @@ func (t *translator) translateStructField(mojomField *mojom_types.StructField) (
 	return
 }
 
+func (t *translator) translateMojomUnion(typeKey string) (m *UnionTemplate) {
+	m = new(UnionTemplate)
+	u := t.GetUserDefinedType(typeKey)
+	union, ok := u.Interface().(mojom_types.MojomUnion)
+	if !ok {
+		log.Panicf("%s is not a union.\n", userDefinedTypeShortName(u))
+	}
+	m.Name = t.goTypeName(typeKey)
+
+	for _, field := range union.Fields {
+		m.Fields = append(m.Fields, t.translateUnionField(&field))
+		m.Fields[len(m.Fields)-1].Union = m
+	}
+
+	return m
+}
+
+func (t *translator) translateUnionField(mojomField *mojom_types.UnionField) (field UnionFieldTemplate) {
+	field.Name = formatName(*mojomField.DeclData.ShortName)
+	field.Type = t.translateType(mojomField.Type)
+	field.Tag = mojomField.Tag
+	field.EncodingInfo = t.encodingInfo(mojomField.Type)
+	field.EncodingInfo.setIdentifier("u.Value")
+	return field
+}
+
 func (t *translator) encodingInfo(mojomType mojom_types.Type) EncodingInfo {
 	return t.encodingInfoNested(mojomType, 0)
 }