Add a command-line flag to enable threaded GPU rasterization.

content/renderer/gpu/compositor_dependencies.h

 // Copyright 2014 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 CONTENT_RENDERER_GPU_COMPOSITOR_DEPENDENCIES_H_
 #define CONTENT_RENDERER_GPU_COMPOSITOR_DEPENDENCIES_H_
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 
@@ skipping 20 matching lines @@
   virtual bool IsGpuRasterizationForced() = 0;
   virtual bool IsGpuRasterizationEnabled() = 0;
   virtual int GetGpuRasterizationMSAASampleCount() = 0;
   virtual bool IsLcdTextEnabled() = 0;
   virtual bool IsDistanceFieldTextEnabled() = 0;
   virtual bool IsZeroCopyEnabled() = 0;
   virtual bool IsOneCopyEnabled() = 0;
   virtual bool IsElasticOverscrollEnabled() = 0;
   // Only valid in single threaded mode.
   virtual bool UseSingleThreadScheduler() = 0;
+  virtual bool IsThreadedGpuRasterizationEnabled() = 0;

[danakj, 2015/02/02 21:48:38]

maybe move this up by other GpuRaster functions?

[vmiura, 2015/02/02 22:03:22]

Done.

   virtual uint32 GetImageTextureTarget() = 0;
   virtual scoped_refptr<base::SingleThreadTaskRunner>
   GetCompositorMainThreadTaskRunner() = 0;
   // Returns null if the compositor is in single-threaded mode (ie. there is no
   // compositor thread).
   virtual scoped_refptr<base::SingleThreadTaskRunner>
   GetCompositorImplThreadTaskRunner() = 0;
   virtual cc::SharedBitmapManager* GetSharedBitmapManager() = 0;
   virtual gpu::GpuMemoryBufferManager* GetGpuMemoryBufferManager() = 0;
   virtual RendererScheduler* GetRendererScheduler() = 0;
   virtual cc::ContextProvider* GetSharedMainThreadContextProvider() = 0;
   virtual scoped_ptr<cc::BeginFrameSource> CreateExternalBeginFrameSource(
       int routing_id) = 0;
 
   virtual ~CompositorDependencies() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_GPU_COMPOSITOR_DEPENDENCIES_H_