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

cc/trees/layer_tree_host.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 <stack>
 #include <string>
 
@@ skipping 682 matching lines @@
 
 void LayerTreeHost::SetVisible(bool visible) {
   if (visible_ == visible)
     return;
   visible_ = visible;
   if (!visible)
     ReduceMemoryUsage();
   proxy_->SetVisible(visible);
 }
 
-void LayerTreeHost::StartPageScaleAnimation(gfx::Vector2d target_offset,
+void LayerTreeHost::StartPageScaleAnimation(const gfx::Vector2d& target_offset,
                                             bool use_anchor,
                                             float scale,
                                             base::TimeDelta duration) {
   pending_page_scale_animation_.reset(new PendingPageScaleAnimation);
   pending_page_scale_animation_->target_offset = target_offset;
   pending_page_scale_animation_->use_anchor = use_anchor;
   pending_page_scale_animation_->scale = scale;
   pending_page_scale_animation_->duration = duration;
 
   SetNeedsCommit();
@@ skipping 558 matching lines @@
   swap_promise_list_.push_back(swap_promise.Pass());
 }
 
 void LayerTreeHost::BreakSwapPromises(SwapPromise::DidNotSwapReason reason) {
   for (size_t i = 0; i < swap_promise_list_.size(); i++)
     swap_promise_list_[i]->DidNotSwap(reason);
   swap_promise_list_.clear();
 }
 
 }  // namespace cc