Implement Paint Containment

third_party/WebKit/Source/core/layout/LayoutInline.cpp

Index: third_party/WebKit/Source/core/layout/LayoutInline.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutInline.cpp b/third_party/WebKit/Source/core/layout/LayoutInline.cpp
index 58f6568fd484ab97715f23e4fbfa2cdac89ef240..383d3c1ffecf6a2ad1d6b5cbdabd55681a78eca8 100644
--- a/third_party/WebKit/Source/core/layout/LayoutInline.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutInline.cpp
@@ -1137,6 +1137,12 @@ LayoutSize LayoutInline::offsetFromContainer(const LayoutObject* container, cons
     return offset;
 }
 
+PaintLayerType LayoutInline::layerTypeRequired() const
+{
+    return isInFlowPositioned() || createsGroup() || hasClipPath() || style()->shouldCompositeForCurrentAnimations()
+        ||  style()->hasCompositorProxy() || style()->containsPaint() ? NormalPaintLayer : NoPaintLayer;

[ojan, 2015/12/10 02:21:40]

Is there a future world in which we don't need a PaintLayer for contained
elements? It's actually an encouraged use of this feature to put it on all the
block elements on a page, but we wouldn't want to create a PaintLayer for each
of them as that's too expensive.

I was going to ask for a TODO to make it not require a layer, but I wasn't sure
what work that would involve.

[chrishtr, 2015/12/10 16:10:52]

PaintLayer may go away in the future in favor of something else, but the things
that make it more heavyweight may or may not.
Well we shouldn't encourage it then...
This is a huge undertaking, right? Stacking contexts are implemented by
PaintLayer.

+}
+
 void LayoutInline::mapLocalToContainer(const LayoutBoxModelObject* paintInvalidationContainer, TransformState& transformState, MapCoordinatesFlags mode, bool* wasFixed, const PaintInvalidationState* paintInvalidationState) const
 {
     if (paintInvalidationContainer == this)