cc: Don't draw and swap if the frame will not change.

cc/output/delegating_renderer_unittest.cc

 // Copyright 2013 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.
 
 #include "cc/output/delegating_renderer.h"
 
 #include "cc/test/fake_output_surface.h"
 #include "cc/test/layer_tree_test.h"
 #include "cc/test/render_pass_test_common.h"
 #include "cc/test/render_pass_test_utils.h"
@@ skipping 25 matching lines @@
 
 class DelegatingRendererTestDraw : public DelegatingRendererTest {
  public:
   virtual void BeginTest() OVERRIDE {
     layer_tree_host()->SetPageScaleFactorAndLimits(1.f, 0.5f, 4.f);
     PostSetNeedsCommitToMainThread();
   }
 
   virtual void AfterTest() OVERRIDE {}
 
-  virtual bool PrepareToDrawOnThread(
-      LayerTreeHostImpl*, LayerTreeHostImpl::FrameData* frame, bool result)
+  virtual bool PrepareToDrawOnThread(LayerTreeHostImpl* host_impl,
+                                     LayerTreeHostImpl::FrameData* frame,
+                                     bool result)
       OVERRIDE {
     EXPECT_EQ(0u, output_surface_->num_sent_frames());
 
     CompositorFrame& last_frame = output_surface_->last_sent_frame();
     EXPECT_FALSE(last_frame.delegated_frame_data);
     EXPECT_FALSE(last_frame.gl_frame_data);
     EXPECT_EQ(0.f, last_frame.metadata.min_page_scale_factor);
     EXPECT_EQ(0.f, last_frame.metadata.max_page_scale_factor);
     return true;
   }
@@ skipping 69 matching lines @@
     EXPECT_EQ(
         15u, last_frame.delegated_frame_data->resource_list.size());
 
     EndTest();
   }
 };
 
 SINGLE_AND_MULTI_THREAD_TEST_F(DelegatingRendererTestResources)
 
 }  // namespace cc