Try to flush DOMStorage too when ending the browsing session.

content/browser/dom_storage/dom_storage_context_wrapper.cc

 // 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.
 
 #include "content/browser/dom_storage/dom_storage_context_wrapper.h"
 
 #include <string>
 #include <vector>
 
 #include "base/bind.h"
@@ skipping 239 matching lines @@
 
 void DOMStorageContextWrapper::Flush() {
   DCHECK(context_.get());
   context_->task_runner()->PostShutdownBlockingTask(
       FROM_HERE, DOMStorageTaskRunner::PRIMARY_SEQUENCE,
       base::Bind(&DOMStorageContextImpl::Flush, context_));
   if (mojo_state_)
     mojo_state_->Flush();
 }
 
+scoped_refptr<base::SequencedTaskRunner>
+DOMStorageContextWrapper::GetSequencedTaskRunner(
+    DOMStorageTaskRunner::SequenceID id) {
+  return context_->task_runner()->GetSequencedTaskRunner(id);
+}
+
 void DOMStorageContextWrapper::OpenLocalStorage(
     const url::Origin& origin,
     mojom::LevelDBWrapperRequest request) {
   if (!mojo_state_)
     return;
   mojo_state_->OpenLocalStorage(origin, std::move(request));
 }
 
 void DOMStorageContextWrapper::OnMemoryPressure(
     base::MemoryPressureListener::MemoryPressureLevel memory_pressure_level) {
@@ skipping 23 matching lines @@
     GetLocalStorageUsageCallback callback,
     std::vector<LocalStorageUsageInfo> usage) {
   context_->task_runner()->PostShutdownBlockingTask(
       FROM_HERE, DOMStorageTaskRunner::PRIMARY_SEQUENCE,
       base::Bind(&GetLocalStorageUsageHelper, base::Passed(&usage),
                  base::RetainedRef(base::ThreadTaskRunnerHandle::Get()),
                  base::RetainedRef(context_), callback));
 }
 
 }  // namespace content