Try to flush DOMStorage too when ending the browsing session.

content/browser/dom_storage/dom_storage_context_wrapper.h

 // Copyright 2013 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 CONTENT_BROWSER_DOM_STORAGE_DOM_STORAGE_CONTEXT_WRAPPER_H_
 #define CONTENT_BROWSER_DOM_STORAGE_DOM_STORAGE_CONTEXT_WRAPPER_H_
 
 #include <map>
 #include <string>
 
 #include "base/macros.h"
 #include "base/memory/memory_coordinator_client.h"
 #include "base/memory/memory_pressure_listener.h"
 #include "base/memory/ref_counted.h"
 #include "content/browser/dom_storage/dom_storage_context_impl.h"
+#include "content/browser/dom_storage/dom_storage_task_runner.h"
 #include "content/common/content_export.h"
 #include "content/common/storage_partition_service.mojom.h"
 #include "content/public/browser/dom_storage_context.h"
 #include "url/origin.h"
 
 namespace base {
 class FilePath;
 }
 
 namespace service_manager {
@@ skipping 38 matching lines @@
 
   // Used by content settings to alter the behavior around
   // what data to keep and what data to discard at shutdown.
   // The policy is not so straight forward to describe, see
   // the implementation for details.
   void SetForceKeepSessionState();
 
   // Called when the BrowserContext/Profile is going away.
   void Shutdown();
 
-  void Flush();
+  // Write any unwritten data to disk, returns a collection of task runners
+  // that have been tasked with writing data.
+  // Note: this method does not sync the data - it only ensures that any
+  // unwritten data has been written out to the filesystem.
+  std::vector<scoped_refptr<base::SequencedTaskRunner>> Flush();
 
   // See mojom::StoragePartitionService interface.
   void OpenLocalStorage(const url::Origin& origin,
                         mojom::LevelDBWrapperRequest request);
 
  private:
   friend class DOMStorageMessageFilter;  // for access to context()
   friend class SessionStorageNamespaceImpl;  // ditto
   friend class base::RefCountedThreadSafe<DOMStorageContextWrapper>;
   friend class MojoDOMStorageBrowserTest;
@@ skipping 21 matching lines @@
   std::unique_ptr<base::MemoryPressureListener> memory_pressure_listener_;
 
   scoped_refptr<DOMStorageContextImpl> context_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(DOMStorageContextWrapper);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DOM_STORAGE_DOM_STORAGE_CONTEXT_WRAPPER_H_