Only allow change-of-basis between transform nodes on the same ancestor chain

cc/trees/property_tree.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_PROPERTY_TREE_H_
 #define CC_TREES_PROPERTY_TREE_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
@@ skipping 147 matching lines @@
   bool Are2DAxisAligned(int source_id, int dest_id) const;
 
   // Updates the parent, target, and screen space transforms and snapping.
   void UpdateTransforms(int id);
 
  private:
   // Returns true iff the node at |desc_id| is a descendant of the node at
   // |anc_id|.
   bool IsDescendant(int desc_id, int anc_id) const;
 
-  // Returns the index of the lowest common ancestor of the nodes |a| and |b|.
-  int LowestCommonAncestor(int a, int b) const;
-
   // Computes the combined transform between |source_id| and |dest_id| and
   // returns false if the inverse of a singular transform was used. These two
   // nodes must be on the same ancestor chain.
   bool CombineTransformsBetween(int source_id,
                                 int dest_id,
                                 gfx::Transform* transform) const;
 
   // Computes the combined inverse transform between |source_id| and |dest_id|
   // and returns false if the inverse of a singular transform was used. These
   // two nodes must be on the same ancestor chain.
@@ skipping 12 matching lines @@
   void UpdateSnapping(TransformNode* node);
 };
 
 class CC_EXPORT ClipTree final : public PropertyTree<ClipNode> {};
 
 class CC_EXPORT OpacityTree final : public PropertyTree<OpacityNode> {};
 
 }  // namespace cc
 
 #endif  // CC_TREES_PROPERTY_TREE_H_