implement the logic to set tile priorities based on current matrix

cc/cc.gyp

 # Copyright (c) 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.
 
 {
   'variables': {
     'cc_source_files': [
       'active_animation.cc',
       'active_animation.h',
       'animation_curve.cc',
@@ skipping 216 matching lines @@
       'thread_impl.cc',
       'thread_impl.h',
       'thread_proxy.cc',
       'thread_proxy.h',
       'tile.cc',
       'tile.h',
       'tile_draw_quad.cc',
       'tile_draw_quad.h',
       'tile_manager.cc',
       'tile_manager.h',
+      'tile_priority.cc',
       'tile_priority.h',
       'tiled_layer.cc',
       'tiled_layer.h',
       'tiled_layer_impl.cc',
       'tiled_layer_impl.h',
       'tiling_data.cc',
       'tiling_data.h',
       'time_source.h',
       'timing_function.cc',
       'timing_function.h',
@@ skipping 37 matching lines @@
       ],
       'all_dependent_settings': {
         'include_dirs': [
           # Needed for <public/WebTransformationMatrix.h> in layer.h
           '<(webkit_src_dir)/Source/Platform/chromium',
         ],
       }
     },
   ],
 }