Creating a helper class for reversing timing functions.

Source/core/animation/CompositorAnimations.h

Index: Source/core/animation/CompositorAnimations.h
diff --git a/Source/core/animation/CompositorAnimations.h b/Source/core/animation/CompositorAnimations.h
index d95196d3a9acc5c26ba155f92282d22097cd5fc1..c80528c9a5702e331d3c6e0b020aac5f15a2599e 100644
--- a/Source/core/animation/CompositorAnimations.h
+++ b/Source/core/animation/CompositorAnimations.h
@@ -39,6 +39,19 @@ namespace WebCore {
 class Element;
 class AnimationEffect;
 
+// Given an input timing function between keyframe at 0 and keyframe at 1.0, we
+// need a timing function such that the behavior with the keyframes swapped is
+// equivalent to reversing time with the input timing function and keyframes.
+// This means flipping the timing function about x=0.5 and about y=0.5.
+// FIXME: Remove once the Compositor natively understands reversing time.
+class CompositorAnimationsTimingFunctionReverser {
+public:
+    static PassRefPtr<TimingFunction> reverse(const LinearTimingFunction* timefunc);
+    static PassRefPtr<TimingFunction> reverse(const CubicBezierTimingFunction* timefunc);
+    static PassRefPtr<TimingFunction> reverse(const ChainedTimingFunction* timefunc);
+    static PassRefPtr<TimingFunction> reverse(const TimingFunction* timefunc);
+};
+
 class CompositorAnimations {
 
 public: