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

cc/layers/tiled_layer.cc

 // Copyright 2011 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/layers/tiled_layer.h"
 
 #include <algorithm>
 #include <vector>
 
 #include "base/auto_reset.h"
@@ skipping 666 matching lines @@
        ++iter) {
     UpdatableTile* tile = static_cast<UpdatableTile*>(iter->second);
     // TODO(enne): This should not ever be null.
     if (!tile)
       continue;
     tile->ResetUpdateState();
   }
 }
 
 namespace {
-gfx::Rect ExpandRectByDelta(const gfx::Rect& rect, gfx::Vector2d delta) {
+gfx::Rect ExpandRectByDelta(const gfx::Rect& rect, const gfx::Vector2d& delta) {
   int width = rect.width() + std::abs(delta.x());
   int height = rect.height() + std::abs(delta.y());
   int x = rect.x() + ((delta.x() < 0) ? delta.x() : 0);
   int y = rect.y() + ((delta.y() < 0) ? delta.y() : 0);
   return gfx::Rect(x, y, width, height);
 }
 }
 
 void TiledLayer::UpdateScrollPrediction() {
   // This scroll prediction is very primitive and should be replaced by a
@@ skipping 213 matching lines @@
   gfx::Rect prepaint_rect = visible_content_rect();
   prepaint_rect.Inset(-tiler_->tile_size().width() * kPrepaintColumns,
                       -tiler_->tile_size().height() * kPrepaintRows);
   gfx::Rect content_rect(content_bounds());
   prepaint_rect.Intersect(content_rect);
 
   return prepaint_rect;
 }
 
 }  // namespace cc