Mojo C++ bindings: add support for UnionTraits.

mojo/public/tools/bindings/generators/mojom_cpp_generator.py

 # Copyright 2013 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.
 
 """Generates C++ source files from a mojom.Module."""
 
 import mojom.generate.generator as generator
 import mojom.generate.module as mojom
 import mojom.generate.pack as pack
 from mojom.generate.template_expander import UseJinja
@@ skipping 350 matching lines @@
   # minus operator doesn't make sense on unsigned types. Doh!
   if kind == mojom.INT32 and token == "-2147483648":
     return "(-%d - 1) /* %s */" % (
         2**31 - 1, "Workaround for MSVC bug; see https://crbug.com/445618")
 
   return "%s%s" % (token, _kind_to_cpp_literal_suffix.get(kind, ""))
 
 def ExpressionToText(value, kind=None):
   return TranslateConstants(value, kind)
 
-def RequiresContextForDataView(struct):
-  for field in struct.fields:
+def RequiresContextForDataView(kind):
+  for field in kind.fields:
     if mojom.IsReferenceKind(field.kind):
       return True
   return False
 
 def ShouldInlineStruct(struct):
   # TODO(darin): Base this on the size of the wrapper class.
   if len(struct.fields) > 4:
     return False
   for field in struct.fields:
     if mojom.IsReferenceKind(field.kind) and not mojom.IsStringKind(field.kind):
@@ skipping 153 matching lines @@
     _use_new_wrapper_types = self.use_new_wrapper_types
     global _variant
     _variant = self.variant
     suffix = "-%s" % self.variant if self.variant else ""
     self.Write(self.GenerateModuleHeader(),
         self.MatchMojomFilePath("%s%s.h" % (self.module.name, suffix)))
     self.Write(self.GenerateModuleInternalHeader(),
         self.MatchMojomFilePath("%s%s-internal.h" % (self.module.name, suffix)))
     self.Write(self.GenerateModuleSource(),
         self.MatchMojomFilePath("%s%s.cc" % (self.module.name, suffix)))