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

cc/trees/layer_tree_host_perftest.cc

 // 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.
 
 #include "cc/trees/layer_tree_host.h"
 
 #include <sstream>
 
 #include "base/file_util.h"
 #include "base/files/file_path.h"
@@ skipping 334 matching lines @@
     // viewport scroll layers as part of its tree setup. The code below is
     // matched to the tree specified in the data file heavy_layer_tree.
     Layer* root = layer_tree_host()->root_layer();
     Layer* clip_layer = root->children()[0];
     Layer* inner_viewport_scroll_layer = clip_layer->children()[0];
     inner_viewport_scroll_layer->SetScrollClipLayerId(root->id());
     inner_viewport_scroll_layer->SetIsContainerForFixedPositionLayers(true);
     layer_tree_host()->RegisterViewportLayers(
         root, inner_viewport_scroll_layer, 0);
   }
-
-  virtual void ApplyScrollAndScale(gfx::Vector2d scroll_delta,
+  virtual void ApplyScrollAndScale(const gfx::Vector2d& scroll_delta,
                                    float scale_delta) OVERRIDE {
     float page_scale_factor = layer_tree_host()->page_scale_factor();
     page_scale_factor *= scale_delta;
     layer_tree_host()->SetPageScaleFactorAndLimits(
         page_scale_factor, min_scale_, max_scale_);
   }
 
   virtual void AnimateLayers(LayerTreeHostImpl* host_impl,
                              base::TimeTicks monotonic_time) OVERRIDE {
     if (!host_impl->pinch_gesture_active()) {
@@ skipping 36 matching lines @@
 
 TEST_F(PageScaleImplSidePaintingPerfTest, HeavyPage) {
   measure_commit_cost_ = true;
   SetTestName("heavy_page_page_scale");
   ReadTestFile("heavy_layer_tree");
   RunTestWithImplSidePainting();
 }
 
 }  // namespace
 }  // namespace cc