Re-land: cc: Implement shared worker contexts.

cc/trees/layer_tree_host.h

 // 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.
 
 #ifndef CC_TREES_LAYER_TREE_HOST_H_
 #define CC_TREES_LAYER_TREE_HOST_H_
 
 #include <limits>
 #include <set>
 #include <string>
@@ skipping 416 matching lines @@
   bool needs_full_tree_sync_;
   bool needs_meta_info_recomputation_;
 
   LayerTreeHostClient* client_;
   scoped_ptr<Proxy> proxy_;
 
   int source_frame_number_;
   int meta_information_sequence_number_;
   scoped_ptr<RenderingStatsInstrumentation> rendering_stats_instrumentation_;
 
+  scoped_ptr<OutputSurface> new_output_surface_;

[danakj, 2015/09/11 19:49:55]

What's the reasoning for these variables? Why own the output surface here? These
own the output surface for the entire time it's used by the compositor? Can you
explain in some comments?

[reveman, 2015/09/11 22:26:13]

This is just moving ownership from the compositor thread to the main thread to
ensure that the output surface is always destroyed on the correct thread. I made
sure current_output_surface_ is reset if init fails and added a comment here in
latest patch. Also updated the description to include the most important part of
this patch: output surfaces now have to be destroyed on the thread they were
created on.

+  scoped_ptr<OutputSurface> current_output_surface_;
   bool output_surface_lost_;
 
   scoped_refptr<Layer> root_layer_;
   scoped_refptr<HeadsUpDisplayLayer> hud_layer_;
 
   base::WeakPtr<InputHandler> input_handler_weak_ptr_;
   base::WeakPtr<TopControlsManager> top_controls_manager_weak_ptr_;
 
   const LayerTreeSettings settings_;
   LayerTreeDebugState debug_state_;
@@ skipping 55 matching lines @@
 
   uint32_t surface_id_namespace_;
   uint32_t next_surface_sequence_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHost);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_H_