Allow to have a transparent UA dependent background.

cc/layers/picture_layer_impl.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_PICTURE_LAYER_IMPL_H_
 #define CC_LAYERS_PICTURE_LAYER_IMPL_H_
 
 #include <stddef.h>
 
 #include <map>
@@ skipping 138 matching lines @@
   float raster_source_scale_;
   float raster_contents_scale_;
   float low_res_raster_contents_scale_;
 
   bool was_screen_space_transform_animating_;
   bool only_used_low_res_last_append_quads_;
   const bool is_mask_;
 
   bool nearest_neighbor_;
 
+  bool has_alpha_channel_;
+
   // Use this instead of |visible_layer_rect()| for tiling calculations. This
   // takes external viewport and transform for tile priority into account.
   gfx::Rect viewport_rect_for_tile_priority_in_content_space_;
 
   gfx::Size gpu_raster_max_texture_size_;
 
   // List of tilings that were used last time we appended quads. This can be
   // used as an optimization not to remove tilings if they are still being
   // drawn. Note that accessing this vector should only be done in the context
   // of comparing pointers, since objects pointed to are not guaranteed to
   // exist.
   std::vector<PictureLayerTiling*> last_append_quads_tilings_;
 
   DISALLOW_COPY_AND_ASSIGN(PictureLayerImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_PICTURE_LAYER_IMPL_H_