[New go generator] Implement declaring unions.

mojom/generators/go/templates/encoding.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 templates
 
-const structEncodingTmplText = `
-{{- define "StructEncodingTmpl" -}}
-{{ $struct := . }}
-func (s *{{$struct.Name}}) Encode(encoder *bindings.Encoder) error {
-        encoder.StartStruct({{$struct.CurVersionSize}}, {{$struct.CurVersionNumber}})
-        {{- range $field := $struct.Fields}}
-                {{ template "FieldEncodingTmpl" $field.EncodingInfo }}
-        {{- end}}
-
-        if err := encoder.Finish(); err != nil {
-                return err
-        }
-        return nil
-}
-{{- end -}}
-`
+import (
+        "text/template"
+)
 
 const fieldEncodingTmplText = `
 {{- define "FieldEncodingTmpl" -}}
 {{- $info := . -}}
 {{- if $info.IsNullable -}}
 if {{$info.Identifier}} == nil {
 {{- if $info.IsPointer -}}
         encoder.WriteNullPointer()
 {{- else if $info.IsHandle -}}
         encoder.WriteInvalidHandle()
@@ skipping 60 matching lines @@
         }
         {{ template "FieldEncodingTmpl" $keyInfo }}
         {{ template "FieldEncodingTmpl" $valueInfo }}
 }
 if err := encoder.Finish(); err != nil {
         return err
 }
 {{- end -}}
 {{- end -}}
 `
+
+func initEncodingTemplates() {
+        template.Must(goFileTmpl.Parse(nonNullableFieldEncodingTmplText))
+        template.Must(goFileTmpl.Parse(fieldEncodingTmplText))
+}