Add needed virtual destructors.

src/utils/win/SkDWriteFontFileStream.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkDWriteFontFileStream_DEFINED
 #define SkDWriteFontFileStream_DEFINED
 
@@ skipping 50 matching lines @@
         void** fragmentContext);
 
     virtual void STDMETHODCALLTYPE ReleaseFileFragment(void* fragmentContext);
     virtual HRESULT STDMETHODCALLTYPE GetFileSize(UINT64* fileSize);
     virtual HRESULT STDMETHODCALLTYPE GetLastWriteTime(UINT64* lastWriteTime);
 
     static HRESULT Create(SkStream* stream, SkDWriteFontFileStreamWrapper** streamFontFileStream);
 
 private:
     explicit SkDWriteFontFileStreamWrapper(SkStream* stream);
+    virtual ~SkDWriteFontFileStreamWrapper() { }
 
     ULONG fRefCount;
     SkAutoTUnref<SkStream> fStream;
     SkMutex fStreamMutex;
 };
 #endif