gpu: Add flag for enabling asynchronous worker context.

cc/trees/layer_tree_settings.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_SETTINGS_H_
 #define CC_TREES_LAYER_TREE_SETTINGS_H_
 
 #include <stddef.h>
 
 #include <vector>
@@ skipping 30 matching lines @@
   // TODO(enne): Remove this after everything uses output surface begin frames.
   bool use_external_begin_frame_source;
   // TODO(enne): Temporary staging for unified begin frame source work.
   bool use_output_surface_begin_frame_source;
   bool main_frame_before_activation_enabled;
   bool using_synchronous_renderer_compositor;
   bool can_use_lcd_text;
   bool use_distance_field_text;
   bool gpu_rasterization_enabled;
   bool gpu_rasterization_forced;
+  bool async_worker_context_enabled;
   int gpu_rasterization_msaa_sample_count;
   float gpu_rasterization_skewport_target_time_in_seconds;
   bool create_low_res_tiling;
 
   enum ScrollbarAnimator {
     NO_ANIMATOR,
     LINEAR_FADE,
     THINNING,
   };
   ScrollbarAnimator scrollbar_animator;
@@ skipping 35 matching lines @@
   // If set to true, the display item list will internally cache a SkPicture for
   // raster rather than directly using the display items.
   bool use_cached_picture_raster;
 
   LayerTreeDebugState initial_debug_state;
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_SETTINGS_H_