cc: add layer usage hint to texture layer

cc/texture_layer.cc

 // Copyright 2010 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 "cc/texture_layer.h"
 
 #include "cc/layer_tree_host.h"
 #include "cc/texture_layer_client.h"
 #include "cc/texture_layer_impl.h"
 #include "cc/thread.h"
 #include "third_party/WebKit/Source/Platform/chromium/public/WebGraphicsContext3D.h"
 
 namespace cc {
 
 static void RunCallbackOnMainThread(
     const TextureMailbox::ReleaseCallback& callback,
     unsigned sync_point) {
   callback.Run(sync_point);
 }
 
 static void PostCallbackToMainThread(
     Thread* main_thread,
     const TextureMailbox::ReleaseCallback& callback,
     unsigned sync_point) {
   main_thread->postTask(
       base::Bind(&RunCallbackOnMainThread, callback, sync_point));
 }
 
-scoped_refptr<TextureLayer> TextureLayer::Create(TextureLayerClient* client) {
-  return scoped_refptr<TextureLayer>(new TextureLayer(client, false));
+scoped_refptr<TextureLayer> TextureLayer::Create(TextureLayerClient* client, bool single_buffer) {
+  return scoped_refptr<TextureLayer>(new TextureLayer(client, false, single_buffer));
 }
 
 scoped_refptr<TextureLayer> TextureLayer::CreateForMailbox() {
-  return scoped_refptr<TextureLayer>(new TextureLayer(NULL, true));
+  return scoped_refptr<TextureLayer>(new TextureLayer(NULL, true, false));
 }
 
-TextureLayer::TextureLayer(TextureLayerClient* client, bool uses_mailbox)
+TextureLayer::TextureLayer(TextureLayerClient* client, bool uses_mailbox, bool single_buffer)
     : Layer(),
       client_(client),
       uses_mailbox_(uses_mailbox),
       flipped_(true),
       uv_top_left_(0.f, 0.f),
       uv_bottom_right_(1.f, 1.f),
       premultiplied_alpha_(true),
       rate_limit_context_(false),
       context_lost_(false),
       texture_id_(0),
       content_committed_(false),
-      own_mailbox_(false) {
+      own_mailbox_(false),
+      single_buffer_(single_buffer) {
   vertex_opacity_[0] = 1.0f;
   vertex_opacity_[1] = 1.0f;
   vertex_opacity_[2] = 1.0f;
   vertex_opacity_[3] = 1.0f;
 }
 
 TextureLayer::~TextureLayer() {
   if (layer_tree_host()) {
     if (texture_id_)
       layer_tree_host()->AcquireLayerTextures();
@@ skipping 125 matching lines @@
         texture_mailbox_.name(), callback, texture_mailbox_.sync_point()));
     own_mailbox_ = false;
   } else {
     texture_layer->setTextureId(texture_id_);
   }
   content_committed_ = DrawsContent();
 }
 
 bool TextureLayer::BlocksPendingCommit() const {
   // Double-buffered texture layers need to be blocked until they can be made
-  // triple-buffered.  Single-buffered layers already prevent draws, so
-  // can block too for simplicity.
-  return DrawsContent();
+  // triple-buffered. Single-buffered layers already prevent draws.
+  if (single_buffer_)
+    return false;
+  else
+    return DrawsContent();
 }
 
 bool TextureLayer::CanClipSelf() const {
   return true;
 }
 
 }  // namespace cc