change backing store cache to be memory-based rather than count

chrome/browser/renderer_host/backing_store_manager.h

 // Copyright (c) 2006-2008 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 CHROME_BROWSER_RENDERER_HOST_BACKING_STORE_MANAGER_H_
 #define CHROME_BROWSER_RENDERER_HOST_BACKING_STORE_MANAGER_H_
 
 #include "base/basictypes.h"
 #include "base/gfx/rect.h"
 #include "base/gfx/size.h"
@@ skipping 45 matching lines @@
   static BackingStore* Lookup(RenderWidgetHost* host);
 
   // Removes the backing store for the host.
   static void RemoveBackingStore(RenderWidgetHost* host);
 
   // Expires the given backing store. This emulates something getting evicted
   // from the cache for the purpose of testing. Returns true if the host was
   // removed, false if it wasn't found.
   static bool ExpireBackingStoreForTest(RenderWidgetHost* host);
 
+  // Current size in bytes of the backing store cache.
+  static size_t MemorySize();
+
  private:
   // Not intended for instantiation.
   BackingStoreManager() {}
 
   DISALLOW_COPY_AND_ASSIGN(BackingStoreManager);
 };
 
 #endif  // CHROME_BROWSER_RENDERER_HOST_BACKING_STORE_MANAGER_H_