cc: Use multiple PrepareTiles approaches

cc/layers/append_quads_data.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_LAYERS_APPEND_QUADS_DATA_H_
 #define CC_LAYERS_APPEND_QUADS_DATA_H_
 
 #include "base/basictypes.h"
 #include "cc/quads/render_pass_id.h"
 
 namespace cc {
 
 struct AppendQuadsData {
   AppendQuadsData()
       : num_incomplete_tiles(0),
         num_missing_tiles(0),
         visible_content_area(0),
         approximated_visible_content_area(0),
-        checkerboarded_visible_content_area(0) {}
+        checkerboarded_visible_content_area(0),
+        raster_source_covers_visible_high_res_tiles(true) {}
 
   // Set by the layer appending quads.
   int64 num_incomplete_tiles;
   // Set by the layer appending quads.
   int64 num_missing_tiles;
   // Set by the layer appending quads.
   int64 visible_content_area;
   // Set by the layer appending quads.
   int64 approximated_visible_content_area;
   // Set by the layer appending quads.
   int64 checkerboarded_visible_content_area;
+  // Set by the layer appending quads.
+  bool raster_source_covers_visible_high_res_tiles;
 };
 
 }  // namespace cc
 #endif  // CC_LAYERS_APPEND_QUADS_DATA_H_