Fix AnimationBase::fractionalTime() to handle a scale of infinity

Source/core/page/animation/KeyframeAnimation.cpp

 /*
  * Copyright (C) 2007, 2012 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 140 matching lines @@
         nextIndex = numKeyframes - 1;
 
     const KeyframeValue& prevKeyframe = m_keyframes[prevIndex];
     const KeyframeValue& nextKeyframe = m_keyframes[nextIndex];
 
     fromStyle = prevKeyframe.style();
     toStyle = nextKeyframe.style();
 
     offset = prevKeyframe.key();
     scale = 1.0 / (nextKeyframe.key() - prevKeyframe.key());
+    // A scale of infinity is handled in AnimationBase::fractionalTime().
+    ASSERT(scale >= 0 && (!std::isinf(scale) || prevIndex == nextIndex));
 
     const TimingFunction* timingFunction = 0;
     if (const CSSAnimationData* matchedAnimation = getAnimationFromStyleByName(fromStyle, name()))
         timingFunction = matchedAnimation->timingFunction().get();
 
     prog = progress(scale, offset, timingFunction);
 }
 
 void KeyframeAnimation::animate(CompositeAnimation*, RenderObject*, const RenderStyle*, RenderStyle* targetStyle, RefPtr<RenderStyle>& animatedStyle)
 {
@@ skipping 296 matching lines @@
 
     if (acceleratedPropertiesOnly) {
         bool isLooping;
         getTimeToNextEvent(t, isLooping);
     }
 
     return t;
 }
 
 } // namespace WebCore