Allow proper highlighting on universal overflow scroll.

Source/core/rendering/compositing/CompositedLayerMapping.cpp

 /*
  * Copyright (C) 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 158 matching lines @@
 CompositedLayerMapping::CompositedLayerMapping(RenderLayer& layer)
     : m_owningLayer(layer)
     , m_artificiallyInflatedBounds(false)
     , m_isMainFrameRenderViewLayer(false)
     , m_requiresOwnBackingStoreForIntrinsicReasons(true)
     , m_requiresOwnBackingStoreForAncestorReasons(true)
     , m_canCompositeFilters(false)
     , m_backgroundLayerPaintsFixedRootBackground(false)
     , m_needToUpdateGraphicsLayer(false)
     , m_needToUpdateGraphicsLayerOfAllDecendants(false)
+    , m_scrollingContentsAreEmpty(false)
 {
     if (layer.isRootLayer() && renderer()->frame()->isMainFrame())
         m_isMainFrameRenderViewLayer = true;
 
     createPrimaryGraphicsLayer();
 }
 
 CompositedLayerMapping::~CompositedLayerMapping()
 {
     // Hits in compositing/squashing/squash-onto-nephew.html.
@@ skipping 860 matching lines @@
             paintPhase |= GraphicsLayerPaintForeground;
         m_scrollingContentsLayer->setPaintingPhase(paintPhase);
     }
 }
 
 void CompositedLayerMapping::updateContentsRect()
 {
     m_graphicsLayer->setContentsRect(pixelSnappedIntRect(contentsBox()));
 }
 
+void CompositedLayerMapping::updateScrollingContentsForSelectionGaps()
+{
+    if (!m_scrollingContentsAreEmpty || !m_scrollingContentsLayer)
+        return;
+
+    // FIXME: in this case, the scrolling contents layer doesn't need to be full size. We should position and size
+    // it more conservatively. See crbug.com/381187.
+    m_scrollingContentsLayer->setDrawsContent(m_owningLayer.rendererHasBlockSelectionGaps() == RenderLayer::LayerHasBlockSelectionGaps);
+}
+
 void CompositedLayerMapping::updateDrawsContent()
 {
     if (m_scrollingLayer) {
         // We don't have to consider overflow controls, because we know that the scrollbars are drawn elsewhere.
         // m_graphicsLayer only needs backing store if the non-scrolling parts (background, outlines, borders, shadows etc) need to paint.
         // m_scrollingLayer never has backing store.
         // m_scrollingContentsLayer only needs backing store if the scrolled contents need to paint.
         bool hasNonScrollingPaintedContent = m_owningLayer.hasVisibleContent() && m_owningLayer.hasBoxDecorationsOrBackground();
         m_graphicsLayer->setDrawsContent(hasNonScrollingPaintedContent);
 
         bool hasScrollingPaintedContent = m_owningLayer.hasVisibleContent() && (renderer()->hasBackground() || paintsChildren());
-        m_scrollingContentsLayer->setDrawsContent(hasScrollingPaintedContent);
+        m_scrollingContentsAreEmpty = !hasScrollingPaintedContent;
+
+        RenderLayer::PresenceOfBlockSelectionGaps hasBlockSelectionGaps = owningLayer().rendererHasBlockSelectionGaps();
+        bool shouldDrawContent = !m_scrollingContentsAreEmpty || hasBlockSelectionGaps == RenderLayer::LayerHasBlockSelectionGaps;
+        m_scrollingContentsLayer->setDrawsContent(shouldDrawContent);
         return;
     }
 
     bool hasPaintedContent = containsPaintedContent();
     if (hasPaintedContent && isAcceleratedCanvas(renderer())) {
         CanvasRenderingContext* context = toHTMLCanvasElement(renderer()->node())->renderingContext();
         // Content layer may be null if context is lost.
         if (blink::WebLayer* contentLayer = context->platformLayer()) {
             Color bgColor(Color::transparent);
             if (contentLayerSupportsDirectBackgroundComposition(renderer())) {
@@ skipping 1174 matching lines @@
     } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
         name = "Scrolling Contents Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore