Run the later parts of startup as UI thread tasks

content/public/common/startup_task_runner.h

+// Copyright (c) 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_STARTUP_TASK_RUNNER_H_
+#define CONTENT_BROWSER_STARTUP_TASK_RUNNER_H_
+
+#include <list>
+
+#include "base/callback.h"
+#include "base/memory/ref_counted.h"
+#include "base/single_thread_task_runner.h"
+
+#include "build/build_config.h"
+
+// This class runs startup tasks.The tasks are either run immediately inline,

[joth, 2013/07/22 16:28:15]

nit: space after stop.

[aberent, 2013/07/22 19:37:40]

Done.

+// or are run one at a time on the UI thread's message loop. The motivation for
+// this is that, on targets where the UI is already started, it allows us to
+// keep the UI responsive during startup.

[joth, 2013/07/22 16:28:15]

nit: I think comment block goes inside namespace immediately before the class
decl.

[aberent, 2013/07/22 19:37:40]

Done.

+
+namespace content {
+
+class StartupTaskRunner : public base::RefCounted<StartupTaskRunner> {

[joth, 2013/07/22 16:28:15]

remind me: why not using SequencedTaskRunner ?
could add a comment here why.

[aberent, 2013/07/22 19:37:40]

I have extended the class comment with a note explaining the difference. This
could (with some changes) possibly have been derived from SequencedTaskRunner,
or more precisely SingleThreadedTaskRunner, but has extra requirements that are
not guaranteed by those, and are not provided by the existing implementations.
It also used in a unique way, so I don't think there would have been any
advantage in doing so from the caller's side.

+ public:
+  class Observer {
+   public:
+    virtual ~Observer() {}
+    // Called when all tasks have been run
+    virtual void AllTasksRun() = 0;

[joth, 2013/07/22 16:28:15]

same comment as the java observer

[aberent, 2013/07/22 19:37:40]

Done.

+  };
+
+  enum StartupMode {
+    IMMEDIATE,
+    INCREMENTAL
+  };
+
+  // Constructor: Note that the observer is optional. The code will check for
+  // a NULL observer before attempting to call observer functions.
+  StartupTaskRunner(StartupMode mode, Observer* observer);
+
+  // Add a task to the queue of startup tasks to be run.
+  virtual void AddTask(base::Closure& callback);
+
+  // Set the task runner to use to run the tasks
+  virtual void SetProxy(
+      const scoped_refptr<base::SingleThreadTaskRunner>& proxy);
+
+  // Start running the tasks.
+  virtual void StartRunningTasks();
+
+ private:
+
+  friend class base::RefCounted<StartupTaskRunner>;
+  virtual ~StartupTaskRunner() {};
+
+  std::list<base::Closure> task_list_;
+  void WrappedTask();
+
+  StartupMode startup_mode_;
+  Observer* observer_;
+  scoped_refptr<base::SingleThreadTaskRunner> proxy_;
+
+  DISALLOW_COPY_AND_ASSIGN(StartupTaskRunner);
+};
+
+}  // namespace content
+#endif  // CONTENT_BROWSER_STARTUP_TASK_RUNNER_H_