Reduce invalidation on children-needs-layout containers

Source/core/rendering/LayoutRepainter.cpp

Index: Source/core/rendering/LayoutRepainter.cpp
diff --git a/Source/core/rendering/LayoutRepainter.cpp b/Source/core/rendering/LayoutRepainter.cpp
index 0e1f7791ce75f65c0d9aed0d2a2077bdb2f42991..a7bfd3143cd5454a80955b308d4a079a19df806c 100644
--- a/Source/core/rendering/LayoutRepainter.cpp
+++ b/Source/core/rendering/LayoutRepainter.cpp
@@ -26,6 +26,7 @@
 #include "config.h"
 #include "core/rendering/LayoutRepainter.h"
 
+#include "core/rendering/RenderBlock.h"
 #include "core/rendering/RenderLayer.h"
 #include "core/rendering/RenderObject.h"
 
@@ -55,6 +56,15 @@ bool LayoutRepainter::repaintAfterLayout()
     if (RuntimeEnabledFeatures::repaintAfterLayoutEnabled())
         return false;
 
+    if (!m_object.needsLayoutBecauseOfChildren()) {
+        // FIXME: We disable the optimization for SVG renderers for now.

[leviw_travelin_and_unemployed, 2014/03/20 21:12:13]

Looking at this and seeing a FIXME about an optimization doesn't immediately
tell me what the optimization is. Instead I have to parse through what's being
checked. How about a static inline method or something that gives this
optimization a name? :)

[Julien - ping for review, 2014/03/20 22:25:33]

Done, named it skipInvalidationWhenLayingOutChildren().

+        // RenderBlock with line boxes are responsible to repaint them so we can't ignore them.
+        bool rendererDisallowOptimization = m_object.isSVG() || (m_object.isRenderBlock() && toRenderBlock(&m_object)->firstLineBox());
+        bool hasEffectVisualOverflow = m_object.style()->hasVisualOverflowingEffect() || m_object.style()->hasOutline();
+        if (!rendererDisallowOptimization && !hasEffectVisualOverflow && !m_object.style()->hasBorder() && !m_object.style()->hasBackground())
+            return false;
+    }
+
     // Hits in compositing/video/video-controls-layer-creation.html
     DisableCompositingQueryAsserts disabler;