Implement "pinned" mode in ash.

ash/common/wm_shell.h

 // 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.
 
 #ifndef ASH_COMMON_WM_SHELL_H_
 #define ASH_COMMON_WM_SHELL_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 57 matching lines @@
   // Returns the root window that newly created windows should be added to.
   // NOTE: this returns the root, newly created window should be added to the
   // appropriate container in the returned window.
   virtual WmWindow* GetRootWindowForNewWindows() = 0;
 
   // Returns true if the first window shown on first run should be
   // unconditionally maximized, overriding the heuristic that normally chooses
   // the window size.
   virtual bool IsForceMaximizeOnFirstRun() = 0;
 
+  // Returns true if a window is currently pinned.
+  virtual bool IsPinned() = 0;
+
   // Returns true if |window| can be shown for the current user. This is
   // intended to check if the current user matches the user associated with
   // |window|.
   // TODO(jamescook): Remove this when ShellDelegate is accessible via this
   // interface.
   virtual bool CanShowWindowForUser(WmWindow* window) = 0;
 
   // See aura::client::CursorClient for details on these.
   virtual void LockCursor() = 0;
   virtual void UnlockCursor() = 0;
@@ skipping 52 matching lines @@
 
   static WmShell* instance_;
 
   std::unique_ptr<WmSystemTrayNotifier> system_tray_notifier_;
   std::unique_ptr<SystemTrayDelegate> system_tray_delegate_;
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_WM_SHELL_H_