Fix the bug that negative outline-offset is covered up by composited

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp

Index: third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
index 8a84bb055d86c9b4bfe9f147a63bdde1442615f0..01e3b74baa51b825493b5a6cf3b5f9b75acbbe81 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
@@ -523,6 +523,10 @@ bool CompositedLayerMapping::updateGraphicsLayerConfiguration() {
           compositor->needsContentsCompositingLayer(&m_owningLayer)))
     layerConfigChanged = true;
 
+  // The decoration layer is currently only used for painting outline
+  if (updateDecorationLayer(layoutObject->style()->hasOutline()))

[flackr, 2016/10/24 17:19:30]

I don't think this condition is specific enough. We only need the decoration
layer for composited overflow scrollers (i.e.
m_owningLayer.getScrollableArea()->usesCompositedScrolling()) with a negative
outline offset that would be covered up by the composited scrolling contents
layer and scrollbars.

[yigu, 2016/10/24 20:31:36]

Done.

+    layerConfigChanged = true;
+
   bool needsDescendantsClippingLayer =
       compositor->clipsCompositingDescendants(&m_owningLayer);
 
@@ -944,6 +948,7 @@ void CompositedLayerMapping::updateGraphicsLayerGeometry(
                           relativeCompositingBounds);
   updateForegroundLayerGeometry(contentsSize, clippingBox);
   updateBackgroundLayerGeometry(contentsSize);
+  updateDecorationLayerGeometry(contentsSize);
   updateScrollingLayerGeometry(localCompositingBounds);
   updateChildClippingMaskLayerGeometry();
 
@@ -1371,6 +1376,20 @@ void CompositedLayerMapping::updateBackgroundLayerGeometry(
       m_graphicsLayer->offsetFromLayoutObject());
 }
 
+void CompositedLayerMapping::updateDecorationLayerGeometry(
+    const FloatSize& relativeCompositingBoundsSize) {
+  if (!m_decorationLayer)
+    return;
+  FloatSize decorationSize = relativeCompositingBoundsSize;
+  m_decorationLayer->setPosition(FloatPoint());
+  if (decorationSize != m_decorationLayer->size()) {
+    m_decorationLayer->setSize(decorationSize);
+    m_decorationLayer->setNeedsDisplay();
+  }
+  m_decorationLayer->setOffsetFromLayoutObject(
+      m_graphicsLayer->offsetFromLayoutObject());
+}
+
 void CompositedLayerMapping::registerScrollingLayers() {
   // Register fixed position layers and their containers with the scrolling
   // coordinator.
@@ -1438,6 +1457,10 @@ void CompositedLayerMapping::updateInternalHierarchy() {
   if (m_layerForScrollCorner)
     m_overflowControlsHostLayer->addChild(m_layerForScrollCorner.get());
 
+  // Now add the DecorationLayer as a subtree to GraphicsLayer
+  bottomLayer = m_graphicsLayer.get();
+  updateBottomLayer(m_decorationLayer.get());
+
   // The squashing containment layer, if it exists, becomes a no-op parent.
   if (m_squashingLayer) {
     ASSERT((m_ancestorClippingLayer && !m_squashingContainmentLayer) ||
@@ -1572,6 +1595,9 @@ void CompositedLayerMapping::updateDrawsContent() {
   if (m_backgroundLayer)
     m_backgroundLayer->setDrawsContent(hasPaintedContent);
 
+  if (m_decorationLayer)
+    m_decorationLayer->setDrawsContent(hasPaintedContent);
+
   if (m_maskLayer)
     m_maskLayer->setDrawsContent(true);
 
@@ -1771,12 +1797,14 @@ enum ApplyToGraphicsLayersModeFlags {
       (1 << 6),  // layers between m_graphicsLayer and children
   ApplyToNonScrollingContentLayers = (1 << 7),
   ApplyToScrollingContentLayers = (1 << 8),
+  ApplyToDecorationLayer = (1 << 9),
   ApplyToAllGraphicsLayers =
       (ApplyToSquashingLayer | ApplyToScrollbarLayers | ApplyToBackgroundLayer |
        ApplyToMaskLayers |
        ApplyToLayersAffectedByPreserve3D |
        ApplyToContentLayers |
-       ApplyToScrollingContentLayers)
+       ApplyToScrollingContentLayers |
+       ApplyToDecorationLayer)
 };
 typedef unsigned ApplyToGraphicsLayersMode;
 
@@ -1839,6 +1867,9 @@ static void ApplyToGraphicsLayers(const CompositedLayerMapping* mapping,
     f(mapping->layerForVerticalScrollbar());
   if ((mode & ApplyToScrollbarLayers) && mapping->layerForScrollCorner())
     f(mapping->layerForScrollCorner());
+
+  if ((mode & ApplyToDecorationLayer) && mapping->decorationLayer())

[flackr, 2016/10/24 20:07:04]

I think you need to apply to non scrolling content layers to get the
invalidation in composited scrolling content, e.g. add:
|| (mode & ApplyToNonScrollingContentLayers)

[yigu, 2016/10/24 20:31:36]

Done.

+    f(mapping->decorationLayer());
 }
 
 struct UpdateRenderingContextFunctor {
@@ -2017,6 +2048,23 @@ bool CompositedLayerMapping::updateBackgroundLayer(bool needsBackgroundLayer) {
   return layerChanged;
 }
 
+bool CompositedLayerMapping::updateDecorationLayer(bool needsDecorationLayer) {
+  bool layerChanged = false;
+  if (needsDecorationLayer) {
+    if (!m_decorationLayer) {
+      m_decorationLayer =
+          createGraphicsLayer(CompositingReasonLayerForDecoration);
+      m_decorationLayer->setPaintingPhase(GraphicsLayerPaintDecoration);
+      layerChanged = true;
+    }
+  } else if (m_decorationLayer) {
+    m_decorationLayer = nullptr;
+    layerChanged = true;
+  }
+
+  return layerChanged;
+}
+
 bool CompositedLayerMapping::updateMaskLayer(bool needsMaskLayer) {
   bool layerChanged = false;
   if (needsMaskLayer) {
@@ -2955,6 +3003,8 @@ void CompositedLayerMapping::paintContents(
     paintLayerFlags |= PaintLayerPaintingOverflowContents;
   if (graphicsLayerPaintingPhase & GraphicsLayerPaintCompositedScroll)
     paintLayerFlags |= PaintLayerPaintingCompositingScrollingPhase;
+  if (graphicsLayerPaintingPhase & GraphicsLayerPaintDecoration)
+    paintLayerFlags |= PaintLayerPaintingCompositingDecorationPhase;
 
   if (graphicsLayer == m_backgroundLayer.get())
     paintLayerFlags |= PaintLayerPaintingRootBackgroundOnly;
@@ -2967,7 +3017,8 @@ void CompositedLayerMapping::paintContents(
       graphicsLayer == m_backgroundLayer.get() ||
       graphicsLayer == m_maskLayer.get() ||
       graphicsLayer == m_childClippingMaskLayer.get() ||
-      graphicsLayer == m_scrollingContentsLayer.get()) {
+      graphicsLayer == m_scrollingContentsLayer.get() ||
+      graphicsLayer == m_decorationLayer.get()) {
     bool paintRootBackgroundOntoScrollingContentsLayer =
         m_backgroundPaintsOntoScrollingContentsLayer;
     DCHECK(!paintRootBackgroundOntoScrollingContentsLayer ||
@@ -3248,6 +3299,8 @@ String CompositedLayerMapping::debugName(
     name = "Scrolling Layer";
   } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
     name = "Scrolling Contents Layer";
+  } else if (graphicsLayer == m_decorationLayer.get()) {
+    name = "Decoration Layer";
   } else {
     ASSERT_NOT_REACHED();
   }