Mark children of an SVG root as needing paint invalidation checking on resize.

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

Index: third_party/WebKit/Source/core/layout/svg/LayoutSVGRoot.cpp
diff --git a/third_party/WebKit/Source/core/layout/svg/LayoutSVGRoot.cpp b/third_party/WebKit/Source/core/layout/svg/LayoutSVGRoot.cpp
index 285aa44af64a71b6c83b90ad5e4e66531e9676bc..beee92bad6166c27a3e5236d8fcaa7b40bf888e1 100644
--- a/third_party/WebKit/Source/core/layout/svg/LayoutSVGRoot.cpp
+++ b/third_party/WebKit/Source/core/layout/svg/LayoutSVGRoot.cpp
@@ -155,6 +155,11 @@ void LayoutSVGRoot::layout() {
   m_isLayoutSizeChanged =
       svg->hasRelativeLengths() && (selfNeedsLayout() || oldSize != size());
 
+  // The scale of one or more of the SVG elements may have changed, so mark
+  // the entire subtree as needing paint invalidation checking.
+  if (m_isLayoutSizeChanged)

[fs, 2016/10/06 10:51:49]

I think this predicate may trigger over-invalidation when the SVG is fixed size,
but a descendant has relative lengths. Could you add a test for that case too?
(I've been trying to pick apart the selfNeedsLayout cases for this layout
object, so I'd like to keep dependencies spelled out if possible.)

[chrishtr, 2016/10/06 20:08:37]

Sorry, I accidentally missed this comment.

Can you paste an example in a reply to this comment? I will turn it into a
layout test.

[fs, 2016/10/06 20:14:46]

Something like resize-svg-invalidate-children.html, but with
width="<somenumber>" and height="<somenumber>" (maybe <somenumber>=100) on the
<svg>, and then width=100% or so on the <rect> ought to do it:

<svg viewBox="0 0 200 200" width="100" height="100">
  <rect width="100%" height="100"/>
</svg>

(and the rest the same.)

+    setMayNeedPaintInvalidationSubtree();
+
   SVGLayoutSupport::layoutChildren(
       firstChild(), false, m_didScreenScaleFactorChange, m_isLayoutSizeChanged);