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

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 9063caf66d67f57c2dad462ec1ec9320663c8369..9ca3b618c456457b8c3f8c9dac50ddb3569579a1 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -428,10 +428,11 @@ void LayerTreeHostImpl::ManageTiles() {
   client_->DidManageTiles();
 }
 
-void LayerTreeHostImpl::StartPageScaleAnimation(gfx::Vector2d target_offset,
-                                                bool anchor_point,
-                                                float page_scale,
-                                                base::TimeDelta duration) {
+void LayerTreeHostImpl::StartPageScaleAnimation(
+    const gfx::Vector2d& target_offset,
+    bool anchor_point,
+    float page_scale,
+    base::TimeDelta duration) {
   if (!RootScrollLayer())
     return;