[#6]Pass gfx structs by const ref (gfx::Vector2d)

cc/trees/layer_tree_host_unittest.cc

 // 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.
 
 #include "cc/trees/layer_tree_host.h"
 
 #include <algorithm>
 
 #include "base/auto_reset.h"
 #include "base/synchronization/lock.h"
@@ skipping 1124 matching lines @@
     }
 
     scroll_layer_->SetScrollable(true);
     scroll_layer_->SetScrollOffset(gfx::Vector2d());
     layer_tree_host()->root_layer()->AddChild(scroll_layer_);
     layer_tree_host()->SetPageScaleFactorAndLimits(1.f, 0.5f, 2.f);
   }
 
   virtual void BeginTest() OVERRIDE { PostSetNeedsCommitToMainThread(); }
 
-  virtual void ApplyScrollAndScale(gfx::Vector2d scroll_delta,
+  virtual void ApplyScrollAndScale(const gfx::Vector2d& scroll_delta,
                                    float scale) OVERRIDE {
     gfx::Vector2d offset = scroll_layer_->scroll_offset();
     scroll_layer_->SetScrollOffset(offset + scroll_delta);
     layer_tree_host()->SetPageScaleFactorAndLimits(scale, 0.5f, 2.f);
   }
 
   virtual void DidActivateTreeOnThread(LayerTreeHostImpl* impl) OVERRIDE {
     // We get one commit before the first draw, and the animation doesn't happen
     // until the second draw.
     switch (impl->active_tree()->source_frame_number()) {
@@ skipping 3791 matching lines @@
 
     EndTest();
   }
 
   virtual void AfterTest() OVERRIDE {}
 };
 
 MULTI_THREAD_TEST_F(LayerTreeHostTestSimpleSwapPromiseMonitor);
 
 }  // namespace cc