Add support for inverse transform animations.

ui/compositor/layer_animation_element.h

 // 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.
 
 #ifndef UI_COMPOSITOR_LAYER_ANIMATION_ELEMENT_H_
 #define UI_COMPOSITOR_LAYER_ANIMATION_ELEMENT_H_
 
 #include <set>
 
 #include "base/time/time.h"
@@ skipping 47 matching lines @@
   LayerAnimationElement(const AnimatableProperties& properties,
                         base::TimeDelta duration);
   virtual ~LayerAnimationElement();
 
   // Creates an element that transitions to the given transform. The caller owns
   // the return value.
   static LayerAnimationElement* CreateTransformElement(
       const gfx::Transform& transform,
       base::TimeDelta duration);
 
+  // Creates an element that counters a transition to the given transform. This
+  // should be used in tandem with an element created with
+  // CreateTransformElement with the same parameters. The caller owns the return
+  // value.
+  static LayerAnimationElement* CreateInverseTransformElement(
+      const gfx::Transform& parent_start,
+      const gfx::Transform& parent_end,
+      base::TimeDelta duration);
+
   // Creates an element that transitions to another in a way determined by an
   // interpolated transform. The element accepts ownership of the interpolated
   // transform. NB: at every step, the interpolated transform clobbers the
   // existing transform. That is, it does not interpolate between the existing
   // transform and the last value the interpolated transform will assume. It is
   // therefore important that the value of the interpolated at time 0 matches
   // the current transform.
   static LayerAnimationElement* CreateInterpolatedTransformElement(
       InterpolatedTransform* interpolated_transform,
       base::TimeDelta duration);
@@ skipping 136 matching lines @@
   int animation_group_id_;
 
   double last_progressed_fraction_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerAnimationElement);
 };
 
 }  // namespace ui
 
 #endif  // UI_COMPOSITOR_LAYER_ANIMATION_ELEMENT_H_