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

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

Index: third_party/WebKit/Source/core/layout/svg/LayoutSVGShape.cpp
diff --git a/third_party/WebKit/Source/core/layout/svg/LayoutSVGShape.cpp b/third_party/WebKit/Source/core/layout/svg/LayoutSVGShape.cpp
index 97ca82c6c64343e01cc3a24ed2ee8df1d20ea80e..0ae8ac70581cfc7e6bd4cb514c5ed9e5b7f27b93 100644
--- a/third_party/WebKit/Source/core/layout/svg/LayoutSVGShape.cpp
+++ b/third_party/WebKit/Source/core/layout/svg/LayoutSVGShape.cpp
@@ -45,6 +45,13 @@
 
 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.