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

cc/layers/layer_impl.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/layers/layer_impl.h"
 
 #include "base/debug/trace_event.h"
 #include "base/json/json_reader.h"
 #include "base/strings/stringprintf.h"
 #include "cc/animation/animation_registrar.h"
@@ skipping 349 matching lines @@
 RenderPass::Id LayerImpl::NextContributingRenderPassId(RenderPass::Id id)
     const {
   return RenderPass::Id(0, 0);
 }
 
 ResourceProvider::ResourceId LayerImpl::ContentsResourceId() const {
   NOTREACHED();
   return 0;
 }
 
-void LayerImpl::SetSentScrollDelta(gfx::Vector2d sent_scroll_delta) {
+void LayerImpl::SetSentScrollDelta(const gfx::Vector2d& sent_scroll_delta) {
   // Pending tree never has sent scroll deltas
   DCHECK(layer_tree_impl()->IsActiveTree());
 
   if (sent_scroll_delta_ == sent_scroll_delta)
     return;
 
   sent_scroll_delta_ = sent_scroll_delta;
 }
 
 gfx::Vector2dF LayerImpl::ScrollBy(const gfx::Vector2dF& scroll) {
@@ skipping 666 matching lines @@
   scroll_offset_delegate_ = scroll_offset_delegate;
   if (scroll_offset_delegate_)
     scroll_offset_delegate_->SetTotalScrollOffset(total_offset);
 }
 
 bool LayerImpl::IsExternalFlingActive() const {
   return scroll_offset_delegate_ &&
          scroll_offset_delegate_->IsExternalFlingActive();
 }
 
-void LayerImpl::SetScrollOffset(gfx::Vector2d scroll_offset) {
+void LayerImpl::SetScrollOffset(const gfx::Vector2d& scroll_offset) {
   SetScrollOffsetAndDelta(scroll_offset, ScrollDelta());
 }
 
-void LayerImpl::SetScrollOffsetAndDelta(gfx::Vector2d scroll_offset,
+void LayerImpl::SetScrollOffsetAndDelta(const gfx::Vector2d& scroll_offset,
                                         const gfx::Vector2dF& scroll_delta) {
   bool changed = false;
 
   last_scroll_offset_ = scroll_offset;
 
   if (scroll_offset_ != scroll_offset) {
     changed = true;
     scroll_offset_ = scroll_offset;
 
     if (scroll_offset_delegate_)
@@ skipping 399 matching lines @@
 
 scoped_ptr<base::Value> LayerImpl::AsValue() const {
   scoped_ptr<base::DictionaryValue> state(new base::DictionaryValue());
   AsValueInto(state.get());
   return state.PassAs<base::Value>();
 }
 
 void LayerImpl::RunMicroBenchmark(MicroBenchmarkImpl* benchmark) {
   benchmark->RunOnLayer(this);
 }
-
 }  // namespace cc