Fix & clarify some comments in compositing. Rename clippedByAncestor to more accurately

Source/core/rendering/compositing/CompositedLayerMapping.h

Index: Source/core/rendering/compositing/CompositedLayerMapping.h
diff --git a/Source/core/rendering/compositing/CompositedLayerMapping.h b/Source/core/rendering/compositing/CompositedLayerMapping.h
index de3cf5afa89870bb391f85bc712a84d4a9467499..84b5b60697c516b917639fec4b0fd181ab6935a4 100644
--- a/Source/core/rendering/compositing/CompositedLayerMapping.h
+++ b/Source/core/rendering/compositing/CompositedLayerMapping.h
@@ -285,7 +285,7 @@ private:
     //  + m_ancestorClippingLayer [OPTIONAL]
     //     + m_graphicsLayer
     //        + m_childContainmentLayer [OPTIONAL] <-OR-> m_scrollingLayer [OPTIONAL] <-OR-> m_childTransformLayer
-    //                                                     + m_scrollingContentsLayer [OPTIONAL]
+    //                                                     + m_scrollingContentsLayer [Present iff m_scrollingLayer is present]
     //
     // We need an ancestor clipping layer if our clipping ancestor is not our ancestor in the
     // clipping tree. Here's what that might look like.
@@ -351,7 +351,7 @@ private:
 
     // A squashing CLM has two possible squashing-related structures.
     //
-    // If m_clippingAncestorLayer is present:
+    // If m_ancestorClippingLayer is present:
     //
     // m_ancestorClippingLayer
     //   + m_graphicsLayer