Clear up session only storage on localstorage shutdown

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>
 
@@ skipping 78 matching lines @@
   // Called on UI thread when the system is under memory pressure.
   void OnMemoryPressure(
       base::MemoryPressureListener::MemoryPressureLevel memory_pressure_level);
 
   // base::MemoryCoordinatorClient implementation:
   void OnPurgeMemory() override;
 
   void PurgeMemory(DOMStorageContextImpl::PurgeOption purge_option);
 
   void GotMojoLocalStorageUsage(GetLocalStorageUsageCallback callback,
+                                base::SingleThreadTaskRunner* reply_task_runner,
                                 std::vector<LocalStorageUsageInfo> usage);
 
   // Keep all mojo-ish details together and not bleed them through the public
   // interface.
-  std::unique_ptr<LocalStorageContextMojo> mojo_state_;

[michaeln, 2017/05/18 23:55:39]

maybe continue using std::unique_ptr<> to document ownership even though we
won't be using the dtor for destruction

oh, nevermind, i see, the dtor is private, maybe comment about the ownership
here?

[Marijn Kruisselbrink, 2017/05/19 00:19:46]

It definitely would be cleanest to somehow have a std::unique_ptr with a custom
deleter that posts a task to the mojo_task_runner_ to call ShutdownAndDelete.
But actually doing that seemed to involve so much code and make things in
general a lot more confusing (due to the need of the deleter to actually know
what task runner to post a task to), so it seemed simpler to just keep it as a
raw pointer, since it's not like random code will ever end up creating
LocalStorageContextMojo instances...

Added more of a comment explaining the ownership at least.

+  LocalStorageContextMojo* mojo_state_ = nullptr;
+  scoped_refptr<base::SingleThreadTaskRunner> mojo_task_runner_;
 
   // To receive memory pressure signals.
   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_