cc: Remove FinishAllRendering, as it doesn't do anything anymore.

cc/output/renderer.h

Index: cc/output/renderer.h
diff --git a/cc/output/renderer.h b/cc/output/renderer.h
index d91e9cd71a8fdd85a0d5f4d56b91df385636ec18..8dadbfb30d301cbe09c91fe1a723cb7abd12ae74 100644
--- a/cc/output/renderer.h
+++ b/cc/output/renderer.h
@@ -75,9 +75,6 @@ class CC_EXPORT Renderer {
                          const gfx::Rect& device_viewport_rect,
                          const gfx::Rect& device_clip_rect) = 0;
 
-  // Waits for rendering to finish.
-  virtual void Finish() = 0;
-
   // Puts backbuffer onscreen.
   virtual void SwapBuffers(CompositorFrameMetadata metadata) = 0;
   virtual void ReclaimResources(const ReturnedResourceArray& resources) {}