mus: Change PointerWatcher to observe all pointer events, with moves optional.

ash/mus/window_manager.h

Index: ash/mus/window_manager.h
diff --git a/ash/mus/window_manager.h b/ash/mus/window_manager.h
index ca857687bde0b77077ede1e2378c4c0e5e4c0bbd..8c2c2430f1d068a99bcf26ac49710e98f19c7345 100644
--- a/ash/mus/window_manager.h
+++ b/ash/mus/window_manager.h
@@ -93,7 +93,8 @@ class WindowManager : public ui::WindowManagerDelegate,
   // WindowTreeClientDelegate:
   void OnEmbed(ui::Window* root) override;
   void OnDidDestroyClient(ui::WindowTreeClient* client) override;
-  void OnEventObserved(const ui::Event& event, ui::Window* target) override;
+  void OnPointerEventObserved(const ui::PointerEvent& event,
+                              ui::Window* target) override;
 
   // WindowManagerDelegate:
   void SetWindowManagerClient(ui::WindowManagerClient* client) override;