[New go generator] Implement declaring unions.

mojom/generators/go/translator/mojom_file.go

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package translator
 
 // TmplFile contains all of the information needed by the templates to generate
 // the go bindings for one mojom file.
 type TmplFile struct {
         PackageName string
         Imports     []Import
         Structs     []*StructTemplate
+        Unions      []*UnionTemplate
 }
 
 type Import struct {
         PackagePath string
         PackageName string
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 
 // StructTemplate contains all of the information needed by the templates to
@@ skipping 39 matching lines @@
 
 // structVersion contains the description of a struct's version.
 type structVersion struct {
         // NumBytes is the size of the struct in bytes at that version.
         NumBytes uint32
 
         // Version is the version number.
         Version uint32
 }
 
+type UnionTemplate struct {
+        // Name is the name of the union in go code.
+        Name string
+
+        // Fields contains the list of fields of the union.
+        Fields []UnionFieldTemplate
+}
+
+type UnionFieldTemplate struct {
+        // Name is the name of the field in go.
+        Name string
+
+        // Type is the go type of the field value.
+        Type string
+
+        // Tag of the field.
+        Tag uint32
+
+        // Union is the union containing this field.
+        Union *UnionTemplate
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 
 // EncodingInfo describes the information necessary to encode a field.
 type EncodingInfo interface {
         // IsSimple returns true if the field is a numeric type, boolean or string.
         IsSimple() bool
 
         // IsHandle returns true if the field is a handle type.
         IsHandle() bool
 
@@ skipping 273 matching lines @@
         return true
 }
 
 func (t *structTypeEncodingInfo) WriteFunction() string {
         panic("Structs don't have a write function.")
 }
 
 func (t *structTypeEncodingInfo) ReadFunction() string {
         panic("Structs don't have a read function.")
 }