[#7] Pass gfx structs by const ref (gfx::Size)

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 620 matching lines @@
     return;
 
   debug_state_ = new_debug_state;
 
   rendering_stats_instrumentation_->set_record_rendering_stats(
       debug_state_.RecordRenderingStats());
 
   SetNeedsCommit();
 }
 
-void LayerTreeHost::SetViewportSize(gfx::Size device_viewport_size) {
+void LayerTreeHost::SetViewportSize(const gfx::Size& device_viewport_size) {
   if (device_viewport_size == device_viewport_size_)
     return;
 
   device_viewport_size_ = device_viewport_size;
 
   SetNeedsCommit();
 }
 
 void LayerTreeHost::SetOverdrawBottomHeight(float overdraw_bottom_height) {
   if (overdraw_bottom_height_ == overdraw_bottom_height)
@@ skipping 620 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