Allow proper highlighting on universal overflow scroll.

Source/core/rendering/RenderLayer.cpp

Index: Source/core/rendering/RenderLayer.cpp
diff --git a/Source/core/rendering/RenderLayer.cpp b/Source/core/rendering/RenderLayer.cpp
index f458c9f1012d87accf86ba99bc0cb4f3f5391235..44ac8f7eb90a5077a439194fec996f88ada0730c 100644
--- a/Source/core/rendering/RenderLayer.cpp
+++ b/Source/core/rendering/RenderLayer.cpp
@@ -3146,9 +3146,16 @@ RenderLayer* RenderLayer::hitTestChildLayerColumns(RenderLayer* childLayer, Rend
     return 0;
 }
 
+void RenderLayer::blockSelectionGapsBoundsChanged()
+{
+    setNeedsCompositingInputsUpdate();
+    compositor()->setNeedsCompositingUpdate(CompositingUpdateAfterCompositingInputChange);
+}
+
 void RenderLayer::addBlockSelectionGapsBounds(const LayoutRect& bounds)
 {
     m_blockSelectionGapsBounds.unite(enclosingIntRect(bounds));
+    blockSelectionGapsBoundsChanged();
 }
 
 void RenderLayer::clearBlockSelectionGapsBounds()
@@ -3156,6 +3163,7 @@ void RenderLayer::clearBlockSelectionGapsBounds()
     m_blockSelectionGapsBounds = IntRect();
     for (RenderLayer* child = firstChild(); child; child = child->nextSibling())
         child->clearBlockSelectionGapsBounds();
+    blockSelectionGapsBoundsChanged();
 }
 
 void RenderLayer::repaintBlockSelectionGaps()
@@ -3179,9 +3187,26 @@ void RenderLayer::repaintBlockSelectionGaps()
         renderer()->invalidatePaintRectangle(rect);
 }
 
+IntRect RenderLayer::blockSelectionGapsBounds() const
+{
+    if (!renderer()->isRenderBlock())
+        return IntRect();
+
+    RenderBlock* renderBlock = toRenderBlock(renderer());
+    LayoutRect gapRects = renderBlock->selectionGapRectsForRepaint(renderBlock);
+
+    return pixelSnappedIntRect(gapRects);
+}
+
 bool RenderLayer::hasBlockSelectionGapBounds() const
 {
-    return !m_blockSelectionGapsBounds.isEmpty();
+    // FIXME: it would be more accurate to return !blockSelectionGapsBounds().isEmpty(), but this is impossible
+    // at the moment because it causes invalid queries to layout-dependent code (crbug.com/372802).

[Julien - ping for review, 2014/06/16 18:30:24]

As mentioned, we should have a lifecycle ASSERT here (either commented or as an
actionable FIXME as it would tell us when we can remove this work-around and use
the more correct !m_blockSelectionGapsBounds()).

[hartmanng, 2014/06/16 19:19:14]

Done.

+
+    if (!renderer()->isRenderBlock())
+        return false;
+
+    return toRenderBlock(renderer())->shouldPaintSelectionGaps();

[abarth-chromium, 2014/06/13 21:55:54]

LGTM, but I'm not 100% sure about these last two stanzas.

[Julien - ping for review, 2014/06/16 18:30:24]

This will yield to false positive as shouldPaintSelectionGaps will return true
for a lot more renderers.

Unfortunately, that's another instance of a chicken-and-egg issue so we have to
use a bigger hammer until it gets fixed :(

 }
 
 bool RenderLayer::intersectsDamageRect(const LayoutRect& layerBounds, const LayoutRect& damageRect, const RenderLayer* rootLayer, const LayoutPoint* offsetFromRoot) const