Add GetStoreSize() to ImageStore to know the actual db size.

components/enhanced_bookmarks/image_store.h

 // Copyright 2014 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 COMPONENTS_ENHANCED_BOOKMARKS_IMAGE_STORE_H_
 #define COMPONENTS_ENHANCED_BOOKMARKS_IMAGE_STORE_H_
 
 #include <map>
 #include <set>
 
@@ skipping 34 matching lines @@
 
   // Populates |urls| with all the urls that have an image in the store.
   virtual void GetAllPageUrls(std::set<GURL>* urls) = 0;
 
   // Removes all images.
   virtual void ClearAll() = 0;
 
   // Moves an image from one url to another.
   void ChangeImageURL(const GURL& from, const GURL& to);
 
+  // Returns the saved images storage size in bytes. If the storage doesn't
+  // exist yet or failed to read, returns -1.
+  virtual int64 GetStoreSizeInBytes() = 0;
+
  protected:
   base::SequenceChecker sequence_checker_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ImageStore);
 };
 
 #endif  // COMPONENTS_ENHANCED_BOOKMARKS_IMAGE_STORE_H_