cc: Derive draw opacity from property trees

cc/trees/draw_property_utils.h

 // Copyright 2014 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_TREES_DRAW_PROPERTY_UTILS_H_
 #define CC_TREES_DRAW_PROPERTY_UTILS_H_
 
 #include "cc/base/cc_export.h"
 
 namespace gfx {
 class Rect;
 class Transform;
 }  // namespace gfx
 
 namespace cc {
 
 class ClipTree;
 class Layer;
+class OpacityTree;
 class TransformTree;
 
 // Computes combined clips for every node in |clip_tree|. This function requires
 // that |transform_tree| has been updated via |ComputeTransforms|.
 // TODO(vollick): ComputeClips and ComputeTransforms will eventually need to be
 // done on both threads.
 void CC_EXPORT
 ComputeClips(ClipTree* clip_tree, const TransformTree& transform_tree);
 
 // Computes combined (screen space) transforms for every node in the transform
 // tree. This must be done prior to calling |ComputeClips|.
 void CC_EXPORT ComputeTransforms(TransformTree* transform_tree);
 
 // Computes the visible content rect for every layer under |root_layer|. The
 // visible content rect is the clipped content space rect that will be used for
 // recording.
 void CC_EXPORT
 ComputeVisibleRectsUsingPropertyTrees(Layer* root_layer,
                                       const Layer* page_scale_layer,
                                       float page_scale_factor,
                                       float device_scale_factor,
                                       const gfx::Rect& viewport,
                                       const gfx::Transform& device_transform,
                                       TransformTree* transform_tree,
-                                      ClipTree* clip_tree);
+                                      ClipTree* clip_tree,
+                                      OpacityTree* opacity_tree);
 
 }  // namespace cc
 
 #endif  // CC_TREES_DRAW_PROPERTY_UTILS_H_