[Offline pages] Introduces TaskQueue to serialize tasks that asynchronously access SQLStore

components/offline_pages/core/task.cc

+// 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.
+
+#include "components/offline_pages/core/task.h"
+
+#include "base/bind.h"
+#include "base/threading/thread_task_runner_handle.h"
+
+namespace offline_pages {
+
+Task::Task() {}
+
+Task::~Task() {}
+
+void Task::SetCompletionCallback(
+    scoped_refptr<base::SingleThreadTaskRunner> runner,
+    const CompletionCallback& callback) {
+  DCHECK(runner);
+  DCHECK(!callback.is_null());
+  completion_runner_ = runner;
+  completion_callback_ = callback;
+}
+
+void Task::Complete() {
+  if (completion_callback_.is_null() || !completion_runner_)
+    return;
+
+  completion_runner_->PostTask(FROM_HERE,
+                               base::Bind(completion_callback_, this));
+}
+
+}  // namespace offline_pages