[#2] Pass gfx structs by const ref (gfx::Rect, gfx::RectF)

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index 0bf71244736cab641726a1b30b5fc66e1c9571a6..55524af0065f84f0717c1094292a6a4f3a6c8a12 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -471,8 +471,9 @@ void LayerTreeHost::DidLoseOutputSurface() {
   SetNeedsCommit();
 }
 
-bool LayerTreeHost::CompositeAndReadback(void* pixels,
-                                         gfx::Rect rect_in_device_viewport) {
+bool LayerTreeHost::CompositeAndReadback(
+    void* pixels,
+    const gfx::Rect& rect_in_device_viewport) {
   trigger_idle_updates_ = false;
   bool ret = proxy_->CompositeAndReadback(pixels, rect_in_device_viewport);
   trigger_idle_updates_ = true;
@@ -541,7 +542,7 @@ void LayerTreeHost::SetNeedsRedraw() {
   SetNeedsRedrawRect(gfx::Rect(device_viewport_size_));
 }
 
-void LayerTreeHost::SetNeedsRedrawRect(gfx::Rect damage_rect) {
+void LayerTreeHost::SetNeedsRedrawRect(const gfx::Rect& damage_rect) {
   proxy_->SetNeedsRedraw(damage_rect);
 }