[#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 b485d0d11fedda7026591bc5e566b1272e88e78a..56850a81c81326e32548310add03158a9e60941a 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -693,7 +693,7 @@ 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.
@@ -1204,5 +1204,4 @@ void Layer::RemoveFromClipTree() {
 void Layer::RunMicroBenchmark(MicroBenchmark* benchmark) {
   benchmark->RunOnLayer(this);
 }
-
 }  // namespace cc