[#5] Pass gfx structs by const ref (gfx::Vector2dF)

cc/input/top_controls_manager.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/input/top_controls_manager.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "cc/animation/keyframed_animation_curve.h"
@@ skipping 80 matching lines @@
 }
 
 void TopControlsManager::ScrollBegin() {
   DCHECK(!pinch_gesture_active_);
   ResetAnimations();
   current_scroll_delta_ = 0.f;
   controls_scroll_begin_offset_ = controls_top_offset_;
 }
 
 gfx::Vector2dF TopControlsManager::ScrollBy(
-    const gfx::Vector2dF pending_delta) {
+    const gfx::Vector2dF& pending_delta) {
   if (pinch_gesture_active_)
     return pending_delta;
 
   if (permitted_state_ == SHOWN && pending_delta.y() > 0)
     return pending_delta;
   else if (permitted_state_ == HIDDEN && pending_delta.y() < 0)
     return pending_delta;
 
   current_scroll_delta_ += pending_delta.y();
 
@@ skipping 130 matching lines @@
 
   if ((animation_direction_ == SHOWING_CONTROLS && new_offset >= 0) ||
       (animation_direction_ == HIDING_CONTROLS
           && new_offset <= -top_controls_height_)) {
     return true;
   }
   return false;
 }
 
 }  // namespace cc