Implement "pinned" mode in ash.

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index bb273232fa20c4616afcb859450cd5083a44f24e..c5ebd097c01bc96af29b152e35ed83eb54c75244 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -172,6 +172,10 @@ namespace test {
 class ShellTestApi;
 }
 
+namespace wm {
+class PinnedController;
+}
+
 // Shell is a singleton object that presents the Shell API and implements the
 // RootWindow's delegate interface.
 //
@@ -588,8 +592,11 @@ class ASH_EXPORT Shell : public SystemModalContainerEventFilterDelegate,
   StickyKeysController* sticky_keys_controller() {
     return sticky_keys_controller_.get();
   }
+
 #endif  // defined(OS_CHROMEOS)
 
+  wm::PinnedController* pinned_controller() { return pinned_controller_.get(); }
+
   ToastManager* toast_manager() { return toast_manager_.get(); }
 
   GPUSupport* gpu_support() { return gpu_support_.get(); }
@@ -730,6 +737,7 @@ class ASH_EXPORT Shell : public SystemModalContainerEventFilterDelegate,
       display_configuration_controller_;
 
   std::unique_ptr<LocaleNotificationController> locale_notification_controller_;
+  std::unique_ptr<wm::PinnedController> pinned_controller_;
 
 #if defined(OS_CHROMEOS)
   std::unique_ptr<PowerEventObserver> power_event_observer_;