Make TransformTree::CombineTransformsBetween run faster

cc/trees/property_tree.cc

 // 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.
 
 #include <set>
 #include <vector>
 
 #include "base/logging.h"
 #include "cc/base/math_util.h"
 #include "cc/trees/property_tree.h"
@@ skipping 130 matching lines @@
   // is a non-linear operation, we cannot use this approach when there is
   // non-trivial flattening between the source and destination nodes. For
   // example, consider the tree R->A->B->C, where B flattens its inherited
   // transform, and A has a non-flat transform. Suppose C is the source and A is
   // the destination. The expected result is C * B. But C's to_screen
   // transform is C * B * flattened(A * R), and A's from_screen transform is
   // R^{-1} * A^{-1}. If at least one of A and R isn't flat, the inverse of
   // flattened(A * R) won't be R^{-1} * A{-1}, so multiplying C's to_screen and
   // A's from_screen will not produce the correct result.
   if (!dest || (dest->data.ancestors_are_invertible &&
-                current->data.node_and_ancestors_are_flat)) {
+                dest->data.node_and_ancestors_are_flat)) {
     transform->ConcatTransform(current->data.to_screen);
     if (dest)
       transform->ConcatTransform(dest->data.from_screen);
     return true;
   }
 
   // Flattening is defined in a way that requires it to be applied while
   // traversing downward in the tree. We first identify nodes that are on the
   // path from the source to the destination (this is traversing upward), and
   // then we visit these nodes in reverse order, flattening as needed. We
@@ skipping 157 matching lines @@
   node->data.from_target.matrix().postTranslate(-translation.x(),
                                                 -translation.y(), 0);
   node->data.to_screen.Translate(translation.x(), translation.y());
   node->data.from_screen.matrix().postTranslate(-translation.x(),
                                                 -translation.y(), 0);
 
   node->data.scroll_snap = translation;
 }
 
 }  // namespace cc