[ServiceWorkerCache] Return the real size of the cache in GetOriginUsage.

content/browser/service_worker/service_worker_cache_storage.h

Index: content/browser/service_worker/service_worker_cache_storage.h
diff --git a/content/browser/service_worker/service_worker_cache_storage.h b/content/browser/service_worker/service_worker_cache_storage.h
index 17757ffc6fc1fd03156e42c3801581a270a49d96..25ab831ab3a0b4922a71e950b95e9cd4732ce00e 100644
--- a/content/browser/service_worker/service_worker_cache_storage.h
+++ b/content/browser/service_worker/service_worker_cache_storage.h
@@ -85,6 +85,10 @@ class CONTENT_EXPORT ServiceWorkerCacheStorage {
 
   void CloseAllCaches();
 
+  // The size of all of the origin's contents in memory. Returns 0 if the cache
+  // backend is not a memory backend.
+  int64 MemoryBackedSize() const;
+
  private:
   class MemoryLoader;
   class SimpleCacheLoader;