Clamp 'zoom' in CSSToLengthConversionData.

Source/core/css/CSSToLengthConversionData.h

 /*
  * Copyright (C) 2013 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 14 matching lines @@
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef CSSToLengthConversionData_h
 #define CSSToLengthConversionData_h
 
 #include "wtf/Assertions.h"
+#include "wtf/MathExtras.h"
 #include "wtf/Noncopyable.h"
+#include <limits>
 
 namespace blink {
 
 class RenderStyle;
 class RenderView;
 class Font;
 
 class CSSToLengthConversionData {
 public:
 
@@ skipping 37 matching lines @@
     float exFontSize() const { return m_fontSizes.ex(); }
     float chFontSize() const { return m_fontSizes.ch(); }
 
     // Accessing these marks the style as having viewport units
     double viewportWidthPercent() const;
     double viewportHeightPercent() const;
     double viewportMinPercent() const;
     double viewportMaxPercent() const;
 
     void setFontSizes(const FontSizes& fontSizes) { m_fontSizes = fontSizes; }
-    void setZoom(float zoom) { m_zoom = zoom; }
+    void setZoom(float zoom) { m_zoom = clampTo<float>(zoom, std::numeric_limits<float>::denorm_min()); }
 
     CSSToLengthConversionData copyWithAdjustedZoom(float newZoom) const
     {
         return CSSToLengthConversionData(m_style, m_fontSizes, m_viewportSize, newZoom);
     }
 
 private:
     const RenderStyle* m_style;
     FontSizes m_fontSizes;
     ViewportSize m_viewportSize;
     float m_zoom;
 };
 
 } // namespace blink
 
 #endif