pdfviewer: fix warnings on mac

experimental/PdfViewer/SkPdfParser.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef SkPdfParser_DEFINED
 #define SkPdfParser_DEFINED
@@ skipping 13 matching lines @@
     PdfContext* fPdfContext;
     SkCanvas* fCanvas;
 
 public:
     PdfTokenLooper(PdfTokenLooper* parent,
                    SkPdfNativeTokenizer* tokenizer,
                    PdfContext* pdfContext,
                    SkCanvas* canvas)
         : fParent(parent), fTokenizer(tokenizer), fPdfContext(pdfContext), fCanvas(canvas) {}
 
+    virtual ~PdfTokenLooper() {}
+
     virtual PdfResult consumeToken(PdfToken& token) = 0;
     virtual void loop() = 0;
 
     void setUp(PdfTokenLooper* parent) {
         fParent = parent;
         fTokenizer = parent->fTokenizer;
         fPdfContext = parent->fPdfContext;
         fCanvas = parent->fCanvas;
     }
 };
@@ skipping 33 matching lines @@
 class SkPdfViewer : public SkRefCnt {
 public:
 
   bool load(const SkString inputFileName, SkPicture* out);
   bool write(void*) const { return false; }
 };
 
 void reportPdfRenderStats();
 
 #endif  // SkPdfParser_DEFINED