Clear up session only storage on localstorage shutdown

content/browser/dom_storage/dom_storage_context_wrapper.h

Index: content/browser/dom_storage/dom_storage_context_wrapper.h
diff --git a/content/browser/dom_storage/dom_storage_context_wrapper.h b/content/browser/dom_storage/dom_storage_context_wrapper.h
index 2c37e330b91a164044bea0da9f7dd3282880a5bd..c8945c24e066cab7ab558f2aff3e340677b5920c 100644
--- a/content/browser/dom_storage/dom_storage_context_wrapper.h
+++ b/content/browser/dom_storage/dom_storage_context_wrapper.h
@@ -96,11 +96,14 @@ class CONTENT_EXPORT DOMStorageContextWrapper :
   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_;
+  // interface. The |mojo_state_| object is owned by this object, but destroyed
+  // asynchronously on the |mojo_task_runner_|.
+  LocalStorageContextMojo* mojo_state_ = nullptr;
+  scoped_refptr<base::SingleThreadTaskRunner> mojo_task_runner_;
 
   // To receive memory pressure signals.
   std::unique_ptr<base::MemoryPressureListener> memory_pressure_listener_;