Introduce Layout*::adjustVisualRectForRasterEffects and use it for SVG hairlines.

third_party/WebKit/Source/core/layout/svg/LayoutSVGShape.cpp

 /*
  * Copyright (C) 2004, 2005, 2007 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2008 Rob Buis <buis@kde.org>
  * Copyright (C) 2005, 2007 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2009 Google, Inc.
  * Copyright (C) 2009 Dirk Schulze <krit@webkit.org>
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  * Copyright (C) 2009 Jeff Schiller <codedread@gmail.com>
  * Copyright (C) 2011 Renata Hodovan <reni@webkit.org>
  * Copyright (C) 2011 University of Szeged
@@ skipping 27 matching lines @@
 #include "core/svg/SVGGeometryElement.h"
 #include "core/svg/SVGLengthContext.h"
 #include "core/svg/SVGPathElement.h"
 #include "platform/geometry/FloatPoint.h"
 #include "platform/graphics/StrokeData.h"
 #include "wtf/MathExtras.h"
 #include "wtf/PtrUtil.h"
 
 namespace blink {
 
+void LayoutSVGShape::adjustVisualRectForRasterEffects(
+    LayoutRect& visualRect) const {
+  // Account for raster expansions due to SVG stroke hairline raster effects.
+  if (styleRef().svgStyle().hasStroke())
+    visualRect.expand(IntRectOutsets(2, 2, 2, 2));

[chrishtr, 2016/10/22 00:01:11]

Because this code doesn't understand anything except the bounding box of the
shape, it is forced
to unconditionally expand the rect.

[Xianzhu, 2016/10/22 00:35:46]

It seems too much to expand by 2 pixels each side.

This could be more precise with:
if (styleRef().svgStyle().hasVisibleStroke()) {
  LayoutUnit pad = 0.5;
  if (styleRef().svgStyle().capStyle() != ButtCap)
    pad += 0.5;
  visualRect.inflate(pad);
}

[chrishtr, 2016/10/22 06:21:04]

Done.

+}
+
 LayoutSVGShape::LayoutSVGShape(SVGGeometryElement* node)
     : LayoutSVGModelObject(node),
       // Default is false, the cached rects are empty from the beginning.
       m_needsBoundariesUpdate(false),
       // Default is true, so we grab a Path object once from SVGGeometryElement.
       m_needsShapeUpdate(true),
       // Default is true, so we grab a AffineTransform object once from
       // SVGGeometryElement.
       m_needsTransformUpdate(true) {}
 
@@ skipping 258 matching lines @@
   return lengthContext.valueForLength(style()->svgStyle().strokeWidth());
 }
 
 LayoutSVGShapeRareData& LayoutSVGShape::ensureRareData() const {
   if (!m_rareData)
     m_rareData = wrapUnique(new LayoutSVGShapeRareData());
   return *m_rareData.get();
 }
 
 }  // namespace blink