Re-land: cc: Implement shared worker contexts.

cc/trees/layer_tree_host.cc

 // Copyright 2011 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/trees/layer_tree_host.h"
 
 #include <algorithm>
 #include <stack>
 #include <string>
 
@@ skipping 367 matching lines @@
     client_->DidCompletePageScaleAnimation();
     did_complete_scale_animation_ = false;
   }
 }
 
 void LayerTreeHost::SetOutputSurface(scoped_ptr<OutputSurface> surface) {
   TRACE_EVENT0("cc", "LayerTreeHost::SetOutputSurface");
   DCHECK(output_surface_lost_);
   DCHECK(surface);
 
-  proxy_->SetOutputSurface(surface.Pass());
+  DCHECK(!new_output_surface_);
+  new_output_surface_ = surface.Pass();
+  proxy_->SetOutputSurface(new_output_surface_.get());
 }
 
 scoped_ptr<OutputSurface> LayerTreeHost::ReleaseOutputSurface() {
   DCHECK(!visible_);
   DCHECK(!output_surface_lost_);
 
   DidLoseOutputSurface();
-  return proxy_->ReleaseOutputSurface();
+  proxy_->ReleaseOutputSurface();
+  return current_output_surface_.Pass();
 }
 
 void LayerTreeHost::RequestNewOutputSurface() {
   client_->RequestNewOutputSurface();
 }
 
 void LayerTreeHost::DidInitializeOutputSurface() {
+  DCHECK(new_output_surface_);
   output_surface_lost_ = false;
+  current_output_surface_ = new_output_surface_.Pass();
   client_->DidInitializeOutputSurface();
 }
 
 void LayerTreeHost::DidFailToInitializeOutputSurface() {
   DCHECK(output_surface_lost_);
+  DCHECK(new_output_surface_);
+  // Note: It is safe to drop all output surface references here as
+  // LayerTreeHostImpl will not keep a pointer to either the old or
+  // new output surface after failing to initialize the new one.
+  current_output_surface_ = nullptr;
+  new_output_surface_ = nullptr;
   client_->DidFailToInitializeOutputSurface();
 }
 
 scoped_ptr<LayerTreeHostImpl> LayerTreeHost::CreateLayerTreeHostImpl(
     LayerTreeHostImplClient* client) {
   DCHECK(proxy_->IsImplThread());
   scoped_ptr<LayerTreeHostImpl> host_impl = LayerTreeHostImpl::Create(
       settings_, client, proxy_.get(), rendering_stats_instrumentation_.get(),
       shared_bitmap_manager_, gpu_memory_buffer_manager_, task_graph_runner_,
       id_);
@@ skipping 797 matching lines @@
   return animation_host_ ? animation_host_->HasAnyAnimation(layer->id())
                          : false;
 }
 
 bool LayerTreeHost::HasActiveAnimation(const Layer* layer) const {
   return animation_host_ ? animation_host_->HasActiveAnimation(layer->id())
                          : false;
 }
 
 }  // namespace cc