Oilpan: make DocumentFragment a heap allocated object.

Source/core/editing/CompositeEditCommand.cpp

Index: Source/core/editing/CompositeEditCommand.cpp
diff --git a/Source/core/editing/CompositeEditCommand.cpp b/Source/core/editing/CompositeEditCommand.cpp
index c3a63e0182483da224fef89aaa4071fcb685dc7f..2fc931b596430fe2600e46391425a5ad677a1b84 100644
--- a/Source/core/editing/CompositeEditCommand.cpp
+++ b/Source/core/editing/CompositeEditCommand.cpp
@@ -1189,7 +1189,7 @@ void CompositeEditCommand::moveParagraphs(const VisiblePosition& startOfParagrap
 
     // FIXME: This is an inefficient way to preserve style on nodes in the paragraph to move. It
     // shouldn't matter though, since moved paragraphs will usually be quite small.
-    RefPtr<DocumentFragment> fragment = startOfParagraphToMove != endOfParagraphToMove ?
+    RefPtrWillBeRawPtr<DocumentFragment> fragment = startOfParagraphToMove != endOfParagraphToMove ?
         createFragmentFromMarkup(document(), createMarkup(range.get(), 0, DoNotAnnotateForInterchange, true, DoNotResolveURLs, constrainingAncestor), "") : nullptr;
 
     // A non-empty paragraph's style is moved when we copy and move it.  We don't move