mash: Port KeyboardUIMus to mojo:ash; remove sysui.

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index bc902c531780f3ac561f6cf0aa9ecbd78af6a19c..d050826b53c4270a58e506f5b2feb30e790ac599 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -385,10 +385,6 @@ class ASH_EXPORT Shell : public SystemModalContainerEventFilterDelegate,
     return is_touch_hud_projection_enabled_;
   }
 
-  // TODO(sky): remove this. This was needed by sysui, but as sysui is going
-  // away it should no longer be needed.
-  bool in_mus() const { return in_mus_; }
-
 #if defined(OS_CHROMEOS)
   // Creates instance of FirstRunHelper. Caller is responsible for deleting
   // returned object.
@@ -560,8 +556,6 @@ class ASH_EXPORT Shell : public SystemModalContainerEventFilterDelegate,
 
   std::unique_ptr<ImmersiveHandlerFactoryAsh> immersive_handler_factory_;
 
-  bool in_mus_ = false;
-
   DISALLOW_COPY_AND_ASSIGN(Shell);
 };