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

cc/layers/layer_impl.cc

Index: cc/layers/layer_impl.cc
diff --git a/cc/layers/layer_impl.cc b/cc/layers/layer_impl.cc
index 7444b7797feb3b4804242b55f7a78fb1449c68c5..f9e9f88fb7ac5f7e88485553b0e5ad8edf0981b6 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -366,7 +366,7 @@ ResourceProvider::ResourceId LayerImpl::ContentsResourceId() const {
   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());
 
@@ -1087,11 +1087,11 @@ bool LayerImpl::IsExternalFlingActive() const {
          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;
 
@@ -1165,7 +1165,7 @@ void LayerImpl::DidBeginTracing() {}
 
 void LayerImpl::ReleaseResources() {}
 
-void LayerImpl::SetMaxScrollOffset(gfx::Vector2d max_scroll_offset) {
+void LayerImpl::SetMaxScrollOffset(const gfx::Vector2d& max_scroll_offset) {
   if (max_scroll_offset_ == max_scroll_offset)
     return;
   max_scroll_offset_ = max_scroll_offset;