Oilpan: tidy up some inter-stack object references.

Source/core/css/parser/CSSParserObserverWrapper.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CSSParserObserverWrapper_h
 #define CSSParserObserverWrapper_h
 
 #include "core/css/parser/CSSParserObserver.h"
 
 namespace blink {
 
 class CSSParserObserverWrapper {
+    STACK_ALLOCATED();
 public:
-    CSSParserObserverWrapper(CSSParserObserver& observer)
-    : m_observer(observer)
+    explicit CSSParserObserverWrapper(CSSParserObserver& observer)
+        : m_observer(observer)
     { }
 
     unsigned startOffset(const CSSParserTokenRange&);
     unsigned previousTokenStartOffset(const CSSParserTokenRange&);
     unsigned endOffset(const CSSParserTokenRange&); // Includes trailing comments
 
     void skipCommentsBefore(const CSSParserTokenRange&, bool leaveDirectlyBefore);
     void yieldCommentsBefore(const CSSParserTokenRange&);
 
     CSSParserObserver& observer() { return m_observer; }
@@ skipping 20 matching lines @@
         unsigned tokensBefore;
     };
 
     Vector<CommentPosition> m_commentOffsets;
     Vector<CommentPosition>::iterator m_commentIterator;
 };
 
 } // namespace blink
 
 #endif // CSSParserObserverWrapper_h