cc: fix content_to_screen_scale in UpdateTilePriorities.

cc/resources/picture_layer_tiling.cc

 // 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.
 
 #include "cc/resources/picture_layer_tiling.h"
 
 #include <algorithm>
 #include <cmath>
 #include <limits>
 
@@ skipping 485 matching lines @@
       << " eventually_rect: " << eventually_rect.ToString();
 
   SetLiveTilesRect(eventually_rect);
 
   last_impl_frame_time_in_seconds_ = current_frame_time_in_seconds;
   last_visible_rect_in_content_space_ = visible_rect_in_content_space;
 
   eviction_tiles_cache_valid_ = false;
 
   TilePriority now_priority(resolution_, TilePriority::NOW, 0);
-  float content_to_screen_scale =
-      1.0f / (contents_scale_ * ideal_contents_scale);
+  float content_to_screen_scale = ideal_contents_scale / contents_scale_;
 
   // Assign now priority to all visible tiles.
   bool include_borders = true;
   has_visible_rect_tiles_ = false;
   for (TilingData::Iterator iter(
            &tiling_data_, visible_rect_in_content_space, include_borders);
        iter;
        ++iter) {
     TileMap::iterator find = tiles_.find(iter.index());
     if (find == tiles_.end())
@@ skipping 555 matching lines @@
   DCHECK(*this);
   do {
     ++current_eviction_tiles_index_;
   } while (current_eviction_tiles_index_ != eviction_tiles_->size() &&
            !(*eviction_tiles_)[current_eviction_tiles_index_]->HasResources());
 
   return *this;
 }
 
 }  // namespace cc