Extract locking behaviour from ProcessSingleton.

chrome/browser/process_singleton_startup_lock.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 CHROME_BROWSER_PROCESS_SINGLETON_STARTUP_LOCK_H_
+#define CHROME_BROWSER_PROCESS_SINGLETON_STARTUP_LOCK_H_
+
+#include <set>
+#include <utility>
+#include <vector>
+
+#include "base/basictypes.h"
+#include "base/command_line.h"
+#include "base/files/file_path.h"
+#include "base/threading/non_thread_safe.h"
+#include "chrome/browser/process_singleton.h"
+
+// Provides a ProcessSingleton::NotificationCallback that can queue up
+// command-line invocations during startup and execute them when startup
+// completes.
+//
+// The object starts in a locked state. |Unlock()| must be called
+// when the process is prepared to handle command-line invocations.
+//
+// Once unlocked, notifications are forwarded to a wrapped NotificationCallback.
+class ProcessSingletonStartupLock : public base::NonThreadSafe {
+ public:
+  explicit ProcessSingletonStartupLock(
+      const ProcessSingleton::NotificationCallback& original_callback);
+  ~ProcessSingletonStartupLock();
+
+  // Returns the callback that should be supplied to ProcessSingleton.

[gab, 2013/03/28 13:45:53]

I don't think this comment should state whom this callback should be passed to
(plus this is not even true in practice as you pass this callback to
ProcessSingletonModalDialogLock, not to ProcessSingleton).

[erikwright (departed), 2013/04/04 01:39:51]

Done.

+  // The callback is only valid during the lifetime of the
+  // ProcessSingletonStartupLock instance.

[gab, 2013/03/28 13:45:53]

I think this "validity" part of the comment is superfluous/confusing as it makes
me feel like the caller should do something about it, but in the use-case this
covers the 2 locks and the ProcessSingleton have the same life span (i.e. the
same as ChromeBrowserMainParts --> forever...).

[erikwright (departed), 2013/04/04 01:39:51]

The caller must be aware of this. It is an error to invoke the callback after
this object destroyed.

+  ProcessSingleton::NotificationCallback AsNotificationCallback();
+
+  // Executes previously queued command-line invocations and allows future
+  // invocations to be executed immediately.
+  void Unlock();
+
+  bool locked() { return locked_; }
+
+ private:
+  typedef std::pair<CommandLine::StringVector, base::FilePath>
+      DelayedStartupMessage;
+
+  bool NotificationCallbackImpl(const CommandLine& command_line,
+                                const base::FilePath& current_directory);
+
+  bool locked_;
+  std::vector<DelayedStartupMessage> saved_startup_messages_;
+  ProcessSingleton::NotificationCallback original_callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(ProcessSingletonStartupLock);
+};
+
+#endif  // CHROME_BROWSER_PROCESS_SINGLETON_STARTUP_LOCK_H_