indexeddb: Removed use of dangling ptr in writeBlobToFileOnIOThread.

content/browser/indexed_db/indexed_db_backing_store.h

Index: content/browser/indexed_db/indexed_db_backing_store.h
diff --git a/content/browser/indexed_db/indexed_db_backing_store.h b/content/browser/indexed_db/indexed_db_backing_store.h
index dd5c758c20a212f5276b9dc77729a90cb4f1d496..7c5710e34e49da2f4f3e8465835a22abf2b50f1a 100644
--- a/content/browser/indexed_db/indexed_db_backing_store.h
+++ b/content/browser/indexed_db/indexed_db_backing_store.h
@@ -459,7 +459,8 @@ class CONTENT_EXPORT IndexedDBBackingStore
       base::Time last_modified_;
     };
 
-    class ChainedBlobWriter : public base::RefCounted<ChainedBlobWriter> {
+    class ChainedBlobWriter
+        : public base::RefCountedThreadSafe<ChainedBlobWriter> {
      public:
       virtual void set_delegate(
           scoped_ptr<fileapi::FileWriterDelegate> delegate) = 0;
@@ -472,7 +473,7 @@ class CONTENT_EXPORT IndexedDBBackingStore
 
      protected:
       virtual ~ChainedBlobWriter() {}
-      friend class base::RefCounted<ChainedBlobWriter>;
+      friend class base::RefCountedThreadSafe<ChainedBlobWriter>;
     };
 
     class ChainedBlobWriterImpl;