cc: Add raster_enabled setting

cc/trees/layer_tree_host_impl.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_IMPL_H_
 #define CC_TREES_LAYER_TREE_HOST_IMPL_H_
 
 #include <set>
 #include <string>
 #include <vector>
@@ skipping 592 matching lines @@
 
   // Resources that were evicted by EvictAllUIResources. Resources are removed
   // from this when they are touched by a create or destroy from the UI resource
   // request queue.
   std::set<UIResourceId> evicted_ui_resources_;
 
   scoped_ptr<OutputSurface> output_surface_;
 
   // |resource_provider_| and |tile_manager_| can be NULL, e.g. when using tile-
   // free rendering - see OutputSurface::ForcedDrawToSoftwareDevice().
+  // |tile_manager_| can also be NULL when raster_enabled is false.
   scoped_ptr<ResourceProvider> resource_provider_;
   scoped_ptr<TileManager> tile_manager_;
   bool use_gpu_rasterization_;
   GpuRasterizationStatus gpu_rasterization_status_;
   scoped_ptr<TileTaskWorkerPool> tile_task_worker_pool_;
   scoped_ptr<Rasterizer> rasterizer_;
   scoped_ptr<ResourcePool> resource_pool_;
   scoped_ptr<ResourcePool> staging_resource_pool_;
   scoped_ptr<Renderer> renderer_;
 
@@ skipping 105 matching lines @@
   bool is_likely_to_require_a_draw_;
 
   scoped_ptr<FrameTimingTracker> frame_timing_tracker_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHostImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_IMPL_H_