Adding a reverse function to the TimingFunctions and tests to prove it works.

Source/core/platform/animation/TimingFunction.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 36 matching lines @@
     virtual ~TimingFunction() { }
 
     Type type() const { return m_type; }
 
     // Evaluates the timing function at the given fraction. The accuracy parameter provides a hint as to the required
     // accuracy and is not guaranteed.
     virtual double evaluate(double fraction, double accuracy) const = 0;
     virtual bool operator==(const TimingFunction& other) const = 0;
     virtual bool operator!=(const TimingFunction& other) const { return !operator==(other); }
 
+    virtual PassRefPtr<TimingFunction> reverse() const = 0;
+
 protected:
     TimingFunction(Type type)
         : m_type(type)
     {
     }
 
 private:
     Type m_type;
 };
 
@@ skipping 11 matching lines @@
         ASSERT(RuntimeEnabledFeatures::webAnimationsEnabled() || (fraction >= 0 && fraction <= 1));
         RELEASE_ASSERT_WITH_MESSAGE(!RuntimeEnabledFeatures::webAnimationsEnabled() || (fraction >= 0 && fraction <= 1), "Web Animations not yet implemented: Timing function behavior outside the range [0, 1] is not yet specified");
         return fraction;
     }
 
     virtual bool operator==(const TimingFunction& other) const
     {
         return other.type() == LinearFunction;
     }
 
+    virtual PassRefPtr<TimingFunction> reverse() const
+    {
+        return const_cast<LinearTimingFunction*>(this);
+    }
+
 private:
     LinearTimingFunction()
         : TimingFunction(LinearFunction)
     {
     }
 };
 
 
 // Forward declare so we can friend it below. Don't used in production code!
 class ChainedTimingFunctionPrintTo;
@@ skipping 79 matching lines @@
         return m_subType == ctf->m_subType;
     }
 
     double x1() const { return m_x1; }
     double y1() const { return m_y1; }
     double x2() const { return m_x2; }
     double y2() const { return m_y2; }
 
     SubType subType() const { return m_subType; }
 
+    virtual PassRefPtr<TimingFunction> reverse() const
+    {
+        switch (m_subType) {
+        case Ease:
+            return const_cast<CubicBezierTimingFunction*>(this);
+        case EaseIn:
+            return preset(EaseOut);
+        case EaseOut:
+            return preset(EaseIn);
+        case EaseInOut:
+            return const_cast<CubicBezierTimingFunction*>(this);
+        case Custom:
+            // Flip the timing function in x. We also have to flip it in y to
+            // maintain the invariant that it runs from (0, 0) to (1, 1).
+            return create(1 - m_x2, 1 - m_y2, 1 - m_x1, 1 - m_y1);
+        default:
+            ASSERT_NOT_REACHED();
+        }
+    }
+
 private:
     explicit CubicBezierTimingFunction(SubType subType, double x1, double y1, double x2, double y2)
         : TimingFunction(CubicBezierFunction)
         , m_x1(x1)
         , m_y1(y1)
         , m_x2(x2)
         , m_y2(y2)
         , m_subType(subType)
     {
     }
@@ skipping 65 matching lines @@
         if (m_subType != Custom)
             return m_subType == stf->m_subType;
         return m_steps == stf->m_steps && m_stepAtStart == stf->m_stepAtStart;
     }
 
     int numberOfSteps() const { return m_steps; }
     bool stepAtStart() const { return m_stepAtStart; }
 
     SubType subType() const { return m_subType; }
 
+    virtual PassRefPtr<TimingFunction> reverse() const
+    {
+        switch (m_subType) {
+        case Start:
+            return preset(End);
+        case End:
+            return preset(Start);
+        case Custom:
+            return create(m_steps, !m_stepAtStart);
+        default:
+            ASSERT_NOT_REACHED();
+            return 0;
+        }
+    }
+
 private:
     StepsTimingFunction(SubType subType, int steps, bool stepAtStart)
         : TimingFunction(StepsFunction)
         , m_steps(steps)
         , m_stepAtStart(stepAtStart)
         , m_subType(subType)
     {
     }
 
     int m_steps;
@@ skipping 40 matching lines @@
         if (ctf->m_segments.size() != m_segments.size())
             return false;
 
         for (size_t i = 0; i < m_segments.size(); i++) {
             if (m_segments[i] != ctf->m_segments[i])
                 return false;
         }
         return true;
     }
 
+    virtual PassRefPtr<TimingFunction> reverse() const
+    {
+        RefPtr<ChainedTimingFunction> reversed = create();
+        for (size_t i = 0; i < m_segments.size(); i++) {
+            size_t index = m_segments.size() - i - 1;
+
+            reversed->appendSegment(1 - m_segments[index].m_min, m_segments[index].m_timingFunction->reverse().get());
+        }
+        return reversed;
+    }
+
 private:
     class Segment {
     public:
         Segment(double min, double max, TimingFunction* timingFunction)
             : m_min(min)
             , m_max(max)
             , m_timingFunction(timingFunction)
         { }
 
         double max() const { return m_max; }
@@ skipping 37 matching lines @@
     Vector<Segment> m_segments;
 
     // Allow printing of our segments. Can be removed once
     // ChainedTimingFunction has a public API for segments.
     friend class ChainedTimingFunctionPrintTo;
 };
 
 } // namespace WebCore
 
 #endif // TimingFunction_h