Converts focusmanager from delegate to observer

components/mus/ws/window_tree_host_impl.h

Index: components/mus/ws/window_tree_host_impl.h
diff --git a/components/mus/ws/window_tree_host_impl.h b/components/mus/ws/window_tree_host_impl.h
index dd7f00323b892af5e366adb9bc9fd53092f7137c..0ecd264fa4bc700d4108f1684b5dd82fbb55e84b 100644
--- a/components/mus/ws/window_tree_host_impl.h
+++ b/components/mus/ws/window_tree_host_impl.h
@@ -12,7 +12,7 @@
 #include "components/mus/ws/display_manager.h"
 #include "components/mus/ws/event_dispatcher.h"
 #include "components/mus/ws/event_dispatcher_delegate.h"
-#include "components/mus/ws/focus_controller_delegate.h"
+#include "components/mus/ws/focus_controller_observer.h"
 #include "components/mus/ws/server_window.h"
 #include "components/mus/ws/server_window_observer.h"
 
@@ -31,7 +31,7 @@ class WindowTreeImpl;
 // deleted.
 class WindowTreeHostImpl : public DisplayManagerDelegate,
                            public mojom::WindowTreeHost,
-                           public FocusControllerDelegate,
+                           public FocusControllerObserver,
                            public EventDispatcherDelegate,
                            public ServerWindowObserver {
  public:
@@ -108,8 +108,9 @@ class WindowTreeHostImpl : public DisplayManagerDelegate,
   void OnTopLevelSurfaceChanged(cc::SurfaceId surface_id) override;
   void OnCompositorFrameDrawn() override;
 
-  // FocusControllerDelegate:
-  void OnFocusChanged(ServerWindow* old_focused_window,
+  // FocusControllerObserver:
+  void OnFocusChanged(FocusControllerChangeSource change_source,
+                      ServerWindow* old_focused_window,
                       ServerWindow* new_focused_window) override;
 
   // EventDispatcherDelegate: