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 041337f6fd6b25e64b4d608d8c43317525dc7f92..1f05fd834c852bed988f10063a40d58bb01652c5 100644
--- a/Source/core/rendering/RenderLayer.cpp
+++ b/Source/core/rendering/RenderLayer.cpp
@@ -3180,9 +3180,16 @@ RenderLayer* RenderLayer::hitTestChildLayerColumns(RenderLayer* childLayer, Rend
     return 0;
 }
 
+void RenderLayer::blockSelectionGapsBoundsChanged()
+{
+    if (needsCompositedScrolling() && hasCompositedLayerMapping())

[Ian Vollick, 2014/06/12 14:54:57]

This looks like a chicken-and-egg thing, but I think it might be avoidable. Can
we schedule a compositing update of the composited-scroll variety and ensure
that the scrolling block selection stuff is freshened during those updates?

[hartmanng, 2014/06/13 14:51:37]

Done.

+        m_compositedLayerMapping->updateScrollingBlockSelection();

[abarth-chromium, 2014/06/13 04:31:05]

Yeah, you should be able to just:

setNeedsCompositingInputsUpdate();
compositor()->setNeedsCompositingUpdate(CompositingUpdateRebuildTree);

If CompositedLayerMapping::updateGraphicsLayerConfiguration were smart enough to
recognize layer change, then you could use
CompositingUpdateAfterCompositingInputChange instead, but the net result would
be the same.

[hartmanng, 2014/06/13 14:51:37]

Would
compositor()->setNeedsCompositingUpdate(CompositingUpdateOnCompositedScroll);
work now that I don't need to mess around with GraphicsLayerTreeBuilder?

+}
+
 void RenderLayer::addBlockSelectionGapsBounds(const LayoutRect& bounds)
 {
     m_blockSelectionGapsBounds.unite(enclosingIntRect(bounds));
+    blockSelectionGapsBoundsChanged();
 }
 
 void RenderLayer::clearBlockSelectionGapsBounds()
@@ -3190,6 +3197,7 @@ void RenderLayer::clearBlockSelectionGapsBounds()
     m_blockSelectionGapsBounds = IntRect();
     for (RenderLayer* child = firstChild(); child; child = child->nextSibling())
         child->clearBlockSelectionGapsBounds();
+    blockSelectionGapsBoundsChanged();
 }
 
 void RenderLayer::repaintBlockSelectionGaps()
@@ -3213,9 +3221,20 @@ void RenderLayer::repaintBlockSelectionGaps()
         renderer()->invalidatePaintRectangle(rect);
 }
 
-bool RenderLayer::hasBlockSelectionGapBounds() const
+IntRect RenderLayer::blockSelectionGapsBounds() const
 {
-    return !m_blockSelectionGapsBounds.isEmpty();
+    if (!renderer()->isRenderBlock())
+        return IntRect();
+
+    RenderBlock* renderBlock = toRenderBlock(renderer());
+    LayoutRect gapRects = renderBlock->selectionGapRectsForRepaint(renderBlock);
+
+    return pixelSnappedIntRect(gapRects);
+}
+
+RenderLayer::PresenceOfBlockSelectionGaps RenderLayer::hasBlockSelectionGapBounds() const
+{
+    return blockSelectionGapsBounds().isEmpty() ? LayerDoesNotHaveBlockSelectionGaps : LayerHasBlockSelectionGaps;
 }
 
 bool RenderLayer::intersectsDamageRect(const LayoutRect& layerBounds, const LayoutRect& damageRect, const RenderLayer* rootLayer, const LayoutPoint* offsetFromRoot) const