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

cc/layers/layer.cc

Index: cc/layers/layer.cc
diff --git a/cc/layers/layer.cc b/cc/layers/layer.cc
index f5850067c415af5bc11f9495d2933533904a32e7..3ca01a741a3ba01ecc728334a3f8c6b0aebadcd0 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -677,7 +677,7 @@ void Layer::RemoveClipChild(Layer* child) {
   SetNeedsCommit();
 }
 
-void Layer::SetScrollOffset(gfx::Vector2d scroll_offset) {
+void Layer::SetScrollOffset(const gfx::Vector2d& scroll_offset) {
   DCHECK(IsPropertyChangeAllowed());
   if (scroll_offset_ == scroll_offset)
     return;
@@ -685,7 +685,7 @@ void Layer::SetScrollOffset(gfx::Vector2d 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.
@@ -700,7 +700,7 @@ void Layer::SetScrollOffsetFromImplSide(gfx::Vector2d scroll_offset) {
   // "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;