Implement Paint Containment

third_party/WebKit/Source/core/paint/PaintLayer.cpp

Index: third_party/WebKit/Source/core/paint/PaintLayer.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.cpp b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
index 71c699920159b8cfb6b664a842bb261c24c6ff37..5b7a5b6e56e267f6b06e757578a24b4872735f19 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
@@ -747,7 +747,7 @@ bool PaintLayer::updateLayerPosition()
     }
 
     // Subtract our parent's scroll offset.
-    if (PaintLayer* positionedParent = layoutObject()->isOutOfFlowPositioned() ? enclosingPositionedAncestor() : nullptr) {
+    if (PaintLayer* positionedParent = layoutObject()->isOutOfFlowPositioned() ? enclosingPositionedOrContainedAncestor() : nullptr) {
         // For positioned layers, we subtract out the enclosing positioned layer's scroll offset.
         if (positionedParent->layoutObject()->hasOverflowClip()) {
             IntSize offset = positionedParent->layoutBox()->scrolledContentOffset();
@@ -818,7 +818,7 @@ static inline bool isFixedPositionedContainer(PaintLayer* layer)
     return layer->isRootLayer() || layer->hasTransformRelatedProperty();
 }
 
-PaintLayer* PaintLayer::enclosingPositionedAncestor(const PaintLayer* ancestor, bool* skippedAncestor) const
+PaintLayer* PaintLayer::enclosingPositionedOrContainedAncestor(const PaintLayer* ancestor, bool* skippedAncestor) const
 {
     ASSERT(!ancestor || skippedAncestor); // If we have specified an ancestor, surely the caller needs to know whether we skipped it.
     if (skippedAncestor)
@@ -1272,7 +1272,7 @@ static inline const PaintLayer* accumulateOffsetTowardsAncestor(const PaintLayer
     PaintLayer* parentLayer;
     if (position == AbsolutePosition || position == FixedPosition) {
         bool foundAncestorFirst;
-        parentLayer = layer->enclosingPositionedAncestor(ancestorLayer, &foundAncestorFirst);
+        parentLayer = layer->enclosingPositionedOrContainedAncestor(ancestorLayer, &foundAncestorFirst);
 
         if (foundAncestorFirst) {
             // Found ancestorLayer before the container of the out-of-flow object, so compute offset
@@ -2358,7 +2358,7 @@ bool PaintLayer::backgroundIsKnownToBeOpaqueInRect(const LayoutRect& localRect)
 
     // We can't consult child layers if we clip, since they might cover
     // parts of the rect that are clipped out.
-    if (layoutObject()->hasOverflowClip())
+    if (layoutObject()->hasOverflowClip() || layoutObject()->style()->containsPaint())
         return false;
 
     return childBackgroundIsKnownToBeOpaqueInRect(localRect);