Add mash shelf application id support.

mash/wm/public/interfaces/user_window_controller.mojom

 // Copyright 2015 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.
 
 module mash.wm.mojom;
 
 struct UserWindow {
   uint32 window_id;
   string window_title;
   bool window_has_focus;
   array<uint8> window_app_icon;  // Serialized SkBitmap.
+  string window_app_id;

[sky, 2016/04/22 15:51:19]

Document this. And while you're at it, document window_id (it's not the same as
the internal id used the ws).

[msw, 2016/04/22 19:02:17]

Done.

 };
 
 // An observer of user windows within mojom::Container::USER_WINDOWS.
 // TODO(msw): Observe focus changes, title/icon changes, etc.
 interface UserWindowObserver {
   // Called when the observer is first added to supply the initial state.
   OnUserWindowObserverAdded(array<UserWindow> user_windows);
 
   OnUserWindowAdded(UserWindow user_window);
   OnUserWindowRemoved(uint32 window_id);
 
   OnUserWindowTitleChanged(uint32 window_id, string window_title);
-  
+
   // |app_icon| is a serialized SkBitmap.
   OnUserWindowAppIconChanged(uint32 window_id, array<uint8> app_icon);
 
   OnUserWindowFocusChanged(uint32 window_id, bool has_focus);
 };
 
 // An interface allowing system UIs to manage the set of user windows.
 // TODO(msw): Add minimization, restoration, opening a chooser view, etc.
 interface UserWindowController {
   AddUserWindowObserver(UserWindowObserver observer);
   FocusUserWindow(uint32 window_id);
 };