Reland of "Remove redundant "layout size changed" state from LayoutSVGRoot"

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 f33a86d98be80e895f1fc642a7b323ff857a92c4..8ba59de14eb4117a0106a1647fe0d635d55468ad 100644
--- a/third_party/WebKit/Source/core/layout/svg/LayoutSVGRoot.cpp
+++ b/third_party/WebKit/Source/core/layout/svg/LayoutSVGRoot.cpp
@@ -153,12 +153,11 @@ void LayoutSVGRoot::layout()
 
     SVGSVGElement* svg = toSVGSVGElement(node());
     ASSERT(svg);
-    m_isLayoutSizeChanged = selfNeedsLayout() || (svg->hasRelativeLengths() && oldSize != size());
     // When hasRelativeLengths() is false, no descendants have relative lengths
     // (hence no one is interested in viewport size changes).
-    bool layoutSizeChanged = m_isLayoutSizeChanged && svg->hasRelativeLengths();
+    m_isLayoutSizeChanged = svg->hasRelativeLengths() && (selfNeedsLayout() || oldSize != size());

[Stephen Chennney, 2016/06/14 20:34:58]

I built a truth table to verify, as this is messy logic. The only change I see
is that now m_isLayoutSizeChanged matches the old values for layoutSizeChanged,
while previously it was also true for (selfNeedsLayout && !hasRelativeLengths).

I agree that there's no point in doing anything if !hasRelativeLengths, so all
of this is a long way of saying I agree with you.

[fs, 2016/06/14 20:46:29]

I guess another tidbit of information that might worth mentioning is that the
"non-local" flag is not read if !hasRelativeLengths - because of how that
relation propagates to ancestors. (The same "guard" is also used in the other
place that sets a flag with the same purpose.)

 
-    SVGLayoutSupport::layoutChildren(firstChild(), false, m_didScreenScaleFactorChange, layoutSizeChanged);
+    SVGLayoutSupport::layoutChildren(firstChild(), false, m_didScreenScaleFactorChange, m_isLayoutSizeChanged);
 
     if (m_needsBoundariesOrTransformUpdate) {
         updateCachedBoundaries();