Make compositingState explicit

Source/core/rendering/RenderBox.cpp

Index: Source/core/rendering/RenderBox.cpp
diff --git a/Source/core/rendering/RenderBox.cpp b/Source/core/rendering/RenderBox.cpp
index 84f11e672d2eb3c9686e9e5df2477c6fd974017a..6ed8e53395f61f6f7aa3b9b69291aa9135cfacc8 100644
--- a/Source/core/rendering/RenderBox.cpp
+++ b/Source/core/rendering/RenderBox.cpp
@@ -1252,7 +1252,8 @@ static bool isCandidateForOpaquenessTest(RenderBox* childBox)
     if (!childBox->width() || !childBox->height())
         return false;
     if (RenderLayer* childLayer = childBox->layer()) {
-        if (childLayer->isComposited())
+        // FIXME: perhaps this could be less conservative?
+        if (childLayer->compositingState() != NotComposited)
             return false;
         // FIXME: Deal with z-index.
         if (!childStyle->hasAutoZIndex())
@@ -1347,7 +1348,7 @@ void RenderBox::paintClippingMask(PaintInfo& paintInfo, const LayoutPoint& paint
     if (!paintInfo.shouldPaintWithinRoot(this) || style()->visibility() != VISIBLE || paintInfo.phase != PaintPhaseClippingMask || paintInfo.context->paintingDisabled())
         return;
 
-    if (!layer() || !layer()->isComposited())
+    if (!layer() || layer()->compositingState() != PaintsIntoOwnBacking)

[Julien - ping for review, 2013/10/03 20:08:36]

How about we add an ASSERT that we never see HasOwnBackingButPaintsIntoAncestor
(per your original comment) as I was going to mention that it was fixing a bug
here?

[shawnsingh, 2013/10/07 11:45:04]

I'm not fixing any bug here, it's just a condition that I already knew would
never happen. The ASSERT is appropriate, so it's added on the latest patch now
=)

         return;
 
     LayoutRect paintRect = LayoutRect(paintOffset, size());