Try to flush DOMStorage too when ending the browsing session.

chrome/browser/browsing_data/browsing_data_remover_impl_unittest.cc

 // Copyright 2017 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.
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <list>
 #include <memory>
 #include <set>
@@ skipping 216 matching lines @@
   }
 
   void ClearHttpAndMediaCaches(
       const base::Time begin,
       const base::Time end,
       const base::Callback<bool(const GURL&)>& url_matcher,
       const base::Closure& callback) override {
     // Not needed in this test.
   }
 
-  void Flush() override {}
+  std::vector<scoped_refptr<base::SequencedTaskRunner>> Flush() override {
+    return std::vector<scoped_refptr<base::SequencedTaskRunner>>();
+  }
 
   void ClearBluetoothAllowedDevicesMapForTesting() override {}
 
   StoragePartitionRemovalData GetStoragePartitionRemovalData() {
     return storage_partition_removal_data_;
   }
 
  private:
   void AsyncRunCallback(const base::Closure& callback) {
     callback.Run();
@@ skipping 1458 matching lines @@
 
   EXPECT_TRUE(remover->is_removing());
 
   // Add one more deletion and wait for it.
   BlockUntilBrowsingDataRemoved(
       base::Time(), base::Time::Max(), BrowsingDataRemover::DATA_TYPE_COOKIES,
       BrowsingDataRemover::ORIGIN_TYPE_UNPROTECTED_WEB);
 
   EXPECT_FALSE(remover->is_removing());
 }