Adjust paint invalidation rects to match the actual radius of rastered blur.

third_party/WebKit/Source/core/style/ShadowData.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, 2009 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 10 matching lines @@
  * Boston, MA 02110-1301, USA.
  *
  */
 
 #ifndef ShadowData_h
 #define ShadowData_h
 
 #include "core/css/StyleColor.h"
 #include "platform/geometry/FloatPoint.h"
 #include "platform/geometry/FloatRectOutsets.h"
+#include "platform/graphics/skia/SkiaUtils.h"
 
 namespace blink {
 
 enum ShadowStyle { Normal, Inset };
 
 // This class holds information about shadows for the text-shadow and box-shadow properties.
 class ShadowData {
     USING_FAST_MALLOC(ShadowData);
 public:
     ShadowData(const FloatPoint& location, float blur, float spread, ShadowStyle style, StyleColor color)
@@ skipping 15 matching lines @@
     FloatPoint location() const { return m_location; }
     float blur() const { return m_blur; }
     float spread() const { return m_spread; }
     ShadowStyle style() const { return m_style; }
     StyleColor color() const { return m_color; }
 
     // Outsets needed to adjust a source rectangle to the one cast by this
     // shadow.
     FloatRectOutsets rectOutsets() const
     {
-        float blurAndSpread = blur() + spread();
+        // 3 * skBlurRadiusToSigma(blur()) is how Skia implements the radius of a blur. See also
+        // https://crbug.com/624175.
+        float blurAndSpread = ceil(3 * skBlurRadiusToSigma(blur())) + spread();
         return FloatRectOutsets(
             blurAndSpread - y() /* top */,
             blurAndSpread + x() /* right */,
             blurAndSpread + y() /* bottom */,
             blurAndSpread - x() /* left */);
     }
 
 private:
     FloatPoint m_location;
     float m_blur;
     float m_spread;
     StyleColor m_color;
     ShadowStyle m_style;
 };
 
 } // namespace blink
 
 #endif // ShadowData_h