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

Source/core/page/animation/AnimationBase.cpp

 /*
  * Copyright (C) 2007, 2008, 2009 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 445 matching lines @@
     if (m_animation->iterationCount() != CSSAnimationData::IterationCountInfinite && !iterationCountHasFractional)
         integralTime = min(integralTime, integralIterationCount - 1);
 
     fractionalTime -= integralTime;
 
     if (((m_animation->direction() == CSSAnimationData::AnimationDirectionAlternate) && (integralTime & 1))
         || ((m_animation->direction() == CSSAnimationData::AnimationDirectionAlternateReverse) && !(integralTime & 1))
         || m_animation->direction() == CSSAnimationData::AnimationDirectionReverse)
         fractionalTime = 1 - fractionalTime;
 
-    if (scale != 1 || offset)
-        fractionalTime = (fractionalTime - offset) * scale;
+    fractionalTime -= offset;
+    // Note that if fractionalTime == 0 here, scale may be infinity, but in
+    // this case we don't need to apply scale anyway.
+    if (scale != 1.0 && fractionalTime) {
+        ASSERT(scale >= 0 && !std::isinf(scale));
+        fractionalTime *= scale;
+    }
 
+    ASSERT(fractionalTime >= 0 && fractionalTime <= 1);
     return fractionalTime;
 }
 
 double AnimationBase::progress(double scale, double offset, const TimingFunction* timingFunction) const
 {
     if (preActive())
         return 0;
 
     double dur = m_animation->duration();
     if (m_animation->iterationCount() > 0)
@@ skipping 93 matching lines @@
         return 0;
 
     double elapsedTime = beginAnimationUpdateTime() - m_startTime;
     // It's possible for the start time to be ahead of the last update time
     // if the compositor has just sent notification for the start of an
     // accelerated animation.
     return max(elapsedTime, 0.0);
 }
 
 } // namespace WebCore