Revert of [#7] Pass gfx structs by const ref (gfx::Size)

cc/trees/occlusion_tracker.h

 // Copyright 2012 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.
 
 #ifndef CC_TREES_OCCLUSION_TRACKER_H_
 #define CC_TREES_OCCLUSION_TRACKER_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
@@ skipping 64 matching lines @@
     return overdraw_metrics_.get();
   }
 
   // Gives the region of the screen that is not occluded by something opaque.
   Region ComputeVisibleRegionInScreen() const {
     DCHECK(!stack_.back().target->parent());
     return SubtractRegions(screen_space_clip_rect_,
                            stack_.back().occlusion_from_inside_target);
   }
 
-  void set_minimum_tracking_size(const gfx::Size& size) {
+  void set_minimum_tracking_size(gfx::Size size) {
     minimum_tracking_size_ = size;
   }
 
   // The following is used for visualization purposes.
   void set_occluding_screen_space_rects_container(
       std::vector<gfx::Rect>* rects) {
     occluding_screen_space_rects_ = rects;
   }
   void set_non_occluding_screen_space_rects_container(
       std::vector<gfx::Rect>* rects) {
@@ skipping 59 matching lines @@
 typedef OcclusionTrackerBase<Layer, RenderSurface> OcclusionTracker;
 typedef OcclusionTrackerBase<LayerImpl, RenderSurfaceImpl> OcclusionTrackerImpl;
 #if !defined(COMPILER_MSVC)
 extern template class OcclusionTrackerBase<Layer, RenderSurface>;
 extern template class OcclusionTrackerBase<LayerImpl, RenderSurfaceImpl>;
 #endif
 
 }  // namespace cc
 
 #endif  // CC_TREES_OCCLUSION_TRACKER_H_