Add support for mojo::TypeConverter to control how convenient conversion should be.

mojo/public/cpp/bindings/tests/sample_service_unittest.cc

 // Copyright 2014 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.
 
 #include <algorithm>
 #include <ostream>
 #include <string>
 
 #include "mojo/public/cpp/bindings/allocation_scope.h"
 #include "mojo/public/cpp/environment/environment.h"
 #include "mojo/public/interfaces/bindings/tests/sample_service.mojom.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace mojo {
 
 template <>
 class TypeConverter<sample::Bar, int32_t> {
  public:
   static int32_t ConvertTo(const sample::Bar& bar) {
     return static_cast<int32_t>(bar.alpha()) << 16 |
            static_cast<int32_t>(bar.beta()) << 8 |
            static_cast<int32_t>(bar.gamma());
   }
+
+  MOJO_ALLOW_IMPLICIT_TYPE_CONVERSION();
 };
 
 }  // namespace mojo
 
 namespace sample {
 namespace {
 
 // Set this variable to true to print the message in hex.
 bool g_dump_message_as_hex = false;
 
@@ skipping 312 matching lines @@
 
   EXPECT_EQ(1u, full.shape_masks().size());
   EXPECT_EQ(1 << imported::SHAPE_RECTANGLE, full.shape_masks()[0]);
 
   EXPECT_EQ(imported::SHAPE_CIRCLE, full.thing().shape());
   EXPECT_EQ(imported::COLOR_BLACK, full.thing().color());
 }
 
 }  // namespace
 }  // namespace sample