Add the future storage framework for the BudgetDatabase.

chrome/browser/budget_service/budget_database.h

+// Copyright 2016 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 CHROME_BROWSER_BUDGET_SERVICE_BUDGET_DATABASE_H_
+#define CHROME_BROWSER_BUDGET_SERVICE_BUDGET_DATABASE_H_
+
+#include <memory>
+
+#include "base/callback_forward.h"
+#include "base/memory/weak_ptr.h"
+#include "base/run_loop.h"
+#include "base/sequenced_task_runner.h"
+#include "components/leveldb_proto/proto_database.h"
+#include "url/gurl.h"
+
+namespace budget_service {
+class Budget;
+}
+
+// A class used to asynchronously read and write details of the budget
+// assigned to service workers. The class uses an underlying levelDB.

[Peter Beverloo, 2016/06/30 13:12:46]

service workers -> origins? Nothing in this class is tied to a particular
Service Worker afaict.

[harkness, 2016/07/01 12:29:54]

Good point. I tend to think of this applying to service workers, because that's
our particular use case, but it could be more generic.

+class BudgetDatabase {
+ public:
+  // The database_dir specifies the location of the budget information on
+  // disk. The task_runner is used by the ProtoDatabase to handle all blocking
+  // calls and disk access.
+  BudgetDatabase(const base::FilePath& database_dir,
+                 const scoped_refptr<base::SequencedTaskRunner>& task_runner);
+  ~BudgetDatabase();
+
+  // Callback for the basic GetBudget call.
+  using GetValueCallback =
+      base::Callback<void(bool success,
+                          std::unique_ptr<budget_service::Budget>)>;
+
+  // Callback for setting a budget value.
+  using SetValueCallback = base::Callback<void(bool success)>;

[Peter Beverloo, 2016/06/30 13:12:46]

micro nit: sorry for missing this earlier— types before methods.

https://google.github.io/styleguide/cppguide.html#Declaration_Order

[harkness, 2016/07/01 12:29:54]

Done.

+
+  void GetValue(const GURL& origin, const GetValueCallback& callback);
+  void SetValue(const GURL& origin,
+                const budget_service::Budget& budget,
+                const SetValueCallback& callback);
+
+ private:
+  void OnDatabaseInit(bool success);

[Peter Beverloo, 2016/06/30 13:12:46]

optional bikeshedding to consider: DidInitializeDatabase?

It's not an event we get from something we observe, but rather the response in
reaction to something we trigger (requesting the database to initialize).

[harkness, 2016/07/01 12:29:54]

I prefer the On* in this case, because I'm planning to do work there (likely
initializing a cache) and that feels more like a response to an event.

+
+  // The database for storing budget information.
+  std::unique_ptr<leveldb_proto::ProtoDatabase<budget_service::Budget>> db_;
+
+  base::WeakPtrFactory<BudgetDatabase> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(BudgetDatabase);
+};
+
+#endif  // CHROME_BROWSER_BUDGET_SERVICE_BUDGET_DATABASE_H_