GPU process clients can perform a "shallow" finish.

cc/output/renderer.h

 // Copyright 2012 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_OUTPUT_RENDERER_H_
 #define CC_OUTPUT_RENDERER_H_
 
 #include "base/basictypes.h"
 #include "cc/base/cc_export.h"
 #include "cc/quads/render_pass.h"
@@ skipping 42 matching lines @@
 
   virtual void DecideRenderPassAllocationsForFrame(
       const RenderPassList& render_passes_in_draw_order) {}
   virtual bool HaveCachedResourcesForRenderPassId(RenderPass::Id id) const;
 
   // This passes ownership of the render passes to the renderer. It should
   // consume them, and empty the list.
   virtual void DrawFrame(RenderPassList* render_passes_in_draw_order) = 0;
 
   // Waits for rendering to finish.
-  virtual void Finish() = 0;
+  //virtual void Finish() = 0;
 
   virtual void DoNoOp() {}
 
   // Puts backbuffer onscreen.
   virtual void SwapBuffers() = 0;
   virtual void ReceiveSwapBuffersAck(const CompositorFrameAck& ack) {}
 
   virtual void GetFramebufferPixels(void* pixels, gfx::Rect rect) = 0;
 
   virtual bool IsContextLost();
 
   virtual void SetVisible(bool visible) = 0;
 
   virtual void SendManagedMemoryStats(size_t bytes_visible,
                                       size_t bytes_visible_and_nearby,
                                       size_t bytes_allocated) = 0;
 
  protected:
   explicit Renderer(RendererClient* client)
       : client_(client) {}
 
   RendererClient* client_;
 
   DISALLOW_COPY_AND_ASSIGN(Renderer);
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_RENDERER_H_