Oilpan: add missing leftmost trace()s for GC mixins.

Source/modules/filesystem/FileWriterSync.h

 /*
  * Copyright (C) 2010 Google Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 41 matching lines @@
     , public ScriptWrappable
     , public WebFileWriterClient {
     DEFINE_WRAPPERTYPEINFO();
     WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(FileWriterSync);
 public:
     static FileWriterSync* create()
     {
         return new FileWriterSync();
     }
     virtual ~FileWriterSync();
+    virtual void trace(Visitor*) override;
 
     // FileWriterBase
     void write(Blob*, ExceptionState&);
     void seek(long long position, ExceptionState&);
     void truncate(long long length, ExceptionState&);
 
     // WebFileWriterClient, via FileWriterBase
     virtual void didWrite(long long bytes, bool complete) override;
     virtual void didTruncate() override;
     virtual void didFail(WebFileError) override;
 
 private:
     FileWriterSync();
     void prepareForWrite();
 
     FileError::ErrorCode m_error;
 #if ENABLE(ASSERT)
     bool m_complete;
 #endif
 };
 
 } // namespace blink
 
-#endif // FileWriter_h
+#endif // FileWriterSync_h