Creating a helper class for reversing timing functions.

Source/core/platform/animation/TimingFunction.h

Index: Source/core/platform/animation/TimingFunction.h
diff --git a/Source/core/platform/animation/TimingFunction.h b/Source/core/platform/animation/TimingFunction.h
index 51e4a9e15e0a5344f2f0d8cb4443db0f3f8281e6..db680aef36fe925301e2842ecbd448e57de9658a 100644
--- a/Source/core/platform/animation/TimingFunction.h
+++ b/Source/core/platform/animation/TimingFunction.h
@@ -281,6 +281,9 @@ private:
         double m_max;
         RefPtr<TimingFunction> m_timingFunction;
 
+        // Allow the compositor to reverse the timing function.
+        friend class CompositorAnimationsTimingFunctionReverser;
+
         // Allow PrintTo/operator== of the segments. Can be removed once
         // ChainedTimingFunction has a public API for segments.
         friend class ChainedTimingFunctionTestHelper;
@@ -294,6 +297,9 @@ private:
 
     Vector<Segment> m_segments;
 
+    // Allow the compositor to reverse the timing function.
+    friend class CompositorAnimationsTimingFunctionReverser;
+
     // Allow PrintTo/operator== of the segments. Can be removed once
     // ChainedTimingFunction has a public API for segments.
     friend class ChainedTimingFunctionTestHelper;