CSSGradientValue should check whether gradientLength is zero or not.

Source/core/css/CSSGradientValue.cpp

 /*
  * Copyright (C) 2008 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 258 matching lines @@
 
             // Radial gradients may need to extend further than the endpoints, because they have
             // to repeat out to the corners of the box.
             if (isRadialGradient()) {
                 if (!computedGradientLength) {
                     FloatSize gradientSize(gradientStart - gradientEnd);
                     gradientLength = gradientSize.diagonalLength();
                 }
 
                 if (maxLengthForRepeat > gradientLength)
-                    maxExtent = maxLengthForRepeat / gradientLength;
+                    maxExtent = gradientLength > 0 ? maxLengthForRepeat / gradientLength : 0;
             }
 
             size_t originalNumStops = numStops;
             size_t originalFirstStopIndex = 0;
 
             // Work backwards from the first, adding stops until we get one before 0.
             float firstOffset = stops[0].offset;
             if (firstOffset > 0) {
                 float currOffset = firstOffset;
                 size_t srcStopOrdinal = originalNumStops - 1;
@@ skipping 874 matching lines @@
         equalHorizontalAndVerticalSize = compareCSSValuePtr(m_endHorizontalSize, other.m_endHorizontalSize) && compareCSSValuePtr(m_endVerticalSize, other.m_endVerticalSize);
     else {
         equalShape = !other.m_shape;
         equalSizingBehavior = !other.m_sizingBehavior;
         equalHorizontalAndVerticalSize = !other.m_endHorizontalSize && !other.m_endVerticalSize;
     }
     return equalShape && equalSizingBehavior && equalHorizontalAndVerticalSize && m_stops == other.m_stops;
 }
 
 } // namespace WebCore