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

cc/layers/layer.cc

 // Copyright 2010 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.h"
 
 #include <algorithm>
 
 #include "base/debug/trace_event.h"
 #include "base/location.h"
@@ skipping 659 matching lines @@
   SetNeedsCommit();
 }
 
 void Layer::RemoveClipChild(Layer* child) {
   clip_children_->erase(child);
   if (clip_children_->empty())
     clip_children_.reset();
   SetNeedsCommit();
 }
 
-void Layer::SetScrollOffset(gfx::Vector2d scroll_offset) {
+void Layer::SetScrollOffset(const gfx::Vector2d& scroll_offset) {
   DCHECK(IsPropertyChangeAllowed());
   if (scroll_offset_ == scroll_offset)
     return;
   scroll_offset_ = scroll_offset;
   SetNeedsCommit();
 }
 
-void Layer::SetScrollOffsetFromImplSide(gfx::Vector2d scroll_offset) {
+void Layer::SetScrollOffsetFromImplSide(const gfx::Vector2d& scroll_offset) {
   DCHECK(IsPropertyChangeAllowed());
   // This function only gets called during a BeginMainFrame, so there
   // is no need to call SetNeedsUpdate here.
   DCHECK(layer_tree_host_ && layer_tree_host_->CommitRequested());
   if (scroll_offset_ == scroll_offset)
     return;
   scroll_offset_ = scroll_offset;
   SetNeedsPushProperties();
   if (!did_scroll_callback_.is_null())
     did_scroll_callback_.Run();
   // The callback could potentially change the layer structure:
   // "this" may have been destroyed during the process.
 }
 
-void Layer::SetMaxScrollOffset(gfx::Vector2d max_scroll_offset) {
+void Layer::SetMaxScrollOffset(const gfx::Vector2d& max_scroll_offset) {
   DCHECK(IsPropertyChangeAllowed());
   if (max_scroll_offset_ == max_scroll_offset)
     return;
   max_scroll_offset_ = max_scroll_offset;
   SetNeedsCommit();
 }
 
 void Layer::SetScrollable(bool scrollable) {
   DCHECK(IsPropertyChangeAllowed());
   if (scrollable_ == scrollable)
@@ skipping 452 matching lines @@
     clip_parent_->RemoveClipChild(this);
 
   clip_parent_ = NULL;
 }
 
 void Layer::RunMicroBenchmark(MicroBenchmark* benchmark) {
   benchmark->RunOnLayer(this);
 }
 
 }  // namespace cc