Return the enclosing composited PaintLayer rather than containingBlock for floats.

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 15577bc0b799cd74df9b336fc57929944c7c05bb..d2992e3928950989b36a96989acb2a1f7f109328 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
@@ -918,8 +918,8 @@ LayoutPoint PaintLayer::computeOffsetFromTransformedAncestor() const {
 }
 
 PaintLayer* PaintLayer::compositingContainer() const {
-  // Floats have special paintinng order. Also, the container does not need
-  // to be a stacking context, because floats are not stacked.
+  // Floats have special painting order, which has complicated semantics.
+  // See the comments around FloatObject::setShouldPaint.
   if (m_layoutObject->isFloating() && m_layoutObject->parent() &&
       !m_layoutObject->parent()->isLayoutBlockFlow())
     return m_layoutObject->containingBlock()->enclosingLayer();