Extract locking behaviour from ProcessSingleton.

chrome/browser/modal_dialog_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_MODAL_DIALOG_LOCK_H_
+#define CHROME_BROWSER_MODAL_DIALOG_LOCK_H_
+
+#include "base/basictypes.h"
+#include "chrome/browser/process_singleton.h"
+#include "ui/gfx/native_widget_types.h"
+
+class CommandLine;
+
+namespace base {
+class FilePath;
+}
+
+// Implements a ProcessSingleton::NotificationCallback that prevents

[gab, 2013/03/27 18:03:26]

I don't like the use of "Implements" here since it not a subclass of a
ProcessSingleton::NotificationCallback, how about "Serves"?

[erikwright (departed), 2013/03/28 03:16:34]

Changed to Provides.

+// command-line handling when a modal dialog is active.
+//
+// While a dialog is active, the ProcessSingleton notification
+// callback will handle but ignore notifications (i.e., neither this process
+// nor the invoking process will handle the command line) and the dialog is
+// brought to the foreground.
+//
+// Otherwise, the notification is forwarded to a wrapped NotificationCallback.
+class ModalDialogLock {

[robertshield, 2013/03/27 14:51:38]

Minor nit, but would prefer naming this with "ProcessSingleton" in the name to
make it immediately obvious to readers that this part of the ProcessSingleton
paraphernalia.

[erikwright (departed), 2013/03/28 03:16:34]

Done.

+ public:
+  explicit ModalDialogLock(
+      const ProcessSingleton::NotificationCallback& original_callback);
+  ~ModalDialogLock();
+
+  // Receives a handle to the active modal dialog, or NULL if the active dialog
+  // is dismissed.
+  void SetActiveModalDialog(gfx::NativeWindow active_dialog);
+
+  // Returns the callback that should be supplied to ProcessSingleton.
+  // The callback is only valid during the lifetime of the ModalDialogLock
+  // instance.
+  ProcessSingleton::NotificationCallback AsNotificationCallback();
+
+ private:
+  bool NotificationCallbackImpl(const CommandLine& command_line,
+                                const base::FilePath& current_directory);
+
+  gfx::NativeWindow active_dialog_;
+  ProcessSingleton::NotificationCallback original_callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(ModalDialogLock);
+};
+
+#endif  // CHROME_BROWSER_MODAL_DIALOG_LOCK_H_