Use gpu::Mailbox in IPCs instead of std::string

ui/compositor/compositor.cc

 // Copyright (c) 2012 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 "ui/compositor/compositor.h"
 
 #include <algorithm>
 #include <deque>
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/memory/singleton.h"
 #include "base/message_loop.h"
-#include "base/string_util.h"
 #include "base/threading/thread.h"
 #include "base/threading/thread_restrictions.h"
 #include "cc/context_provider.h"
 #include "cc/input_handler.h"
 #include "cc/layer.h"
 #include "cc/layer_tree_host.h"
 #include "cc/output_surface.h"
 #include "cc/thread_impl.h"
+#include "gpu/command_buffer/common/mailbox.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "ui/compositor/compositor_observer.h"
 #include "ui/compositor/compositor_switches.h"
 #include "ui/compositor/dip_util.h"
 #include "ui/compositor/layer.h"
 #include "ui/compositor/test_web_graphics_context_3d.h"
 #include "ui/gl/gl_context.h"
 #include "ui/gl/gl_implementation.h"
 #include "ui/gl/gl_surface.h"
 #include "ui/gl/gl_switches.h"
@@ skipping 245 matching lines @@
 
 Texture::Texture(bool flipped, const gfx::Size& size, float device_scale_factor)
     : size_(size),
       flipped_(flipped),
       device_scale_factor_(device_scale_factor) {
 }
 
 Texture::~Texture() {
 }
 
-std::string Texture::Produce() {
-  return EmptyString();
+gpu::Mailbox Texture::Produce() {
+  return gpu::Mailbox();
 }
 
 CompositorLock::CompositorLock(Compositor* compositor)
     : compositor_(compositor) {
   MessageLoop::current()->PostDelayedTask(
       FROM_HERE,
       base::Bind(&CompositorLock::CancelLock, AsWeakPtr()),
       base::TimeDelta::FromMilliseconds(kCompositorLockTimeoutMs));
 }
 
@@ skipping 393 matching lines @@
 COMPOSITOR_EXPORT void DisableTestCompositor() {
   ResetImplicitFactory();
   g_test_compositor_enabled = false;
 }
 
 COMPOSITOR_EXPORT bool IsTestCompositorEnabled() {
   return g_test_compositor_enabled;
 }
 
 }  // namespace ui