Allow proper highlighting on universal overflow scroll.

Source/core/rendering/RenderLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 3128 matching lines @@
             }
 
             if (hitLayer)
                 return hitLayer;
         }
     }
 
     return 0;
 }
 
+void RenderLayer::blockSelectionGapsBoundsChanged()
+{
+    setNeedsCompositingInputsUpdate();
+    compositor()->setNeedsCompositingUpdate(CompositingUpdateAfterCompositingInputChange);
+}
+
 void RenderLayer::addBlockSelectionGapsBounds(const LayoutRect& bounds)
 {
     m_blockSelectionGapsBounds.unite(enclosingIntRect(bounds));
+    blockSelectionGapsBoundsChanged();
 }
 
 void RenderLayer::clearBlockSelectionGapsBounds()
 {
     m_blockSelectionGapsBounds = IntRect();
     for (RenderLayer* child = firstChild(); child; child = child->nextSibling())
         child->clearBlockSelectionGapsBounds();
+    blockSelectionGapsBoundsChanged();
 }
 
 void RenderLayer::repaintBlockSelectionGaps()
 {
     for (RenderLayer* child = firstChild(); child; child = child->nextSibling())
         child->repaintBlockSelectionGaps();
 
     if (m_blockSelectionGapsBounds.isEmpty())
         return;
 
     LayoutRect rect = m_blockSelectionGapsBounds;
     if (renderer()->hasOverflowClip()) {
         RenderBox* box = renderBox();
         rect.move(-box->scrolledContentOffset());
         if (!scrollableArea()->usesCompositedScrolling())
             rect.intersect(box->overflowClipRect(LayoutPoint()));
     }
     if (renderer()->hasClip())
         rect.intersect(toRenderBox(renderer())->clipRect(LayoutPoint()));
     if (!rect.isEmpty())
         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
 {
     // Always examine the canvas and the root.
     // FIXME: Could eliminate the isDocumentElement() check if we fix background painting so that the RenderView
     // paints the root's background.
     if (isRootLayer() || renderer()->isDocumentElement())
         return true;
 
@@ skipping 635 matching lines @@
     }
 }
 
 void showLayerTree(const WebCore::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif