Update ui::PointerEvent to support mouse wheel and capture change events.

ui/views/pointer_watcher.h

Index: ui/views/pointer_watcher.h
diff --git a/ui/views/pointer_watcher.h b/ui/views/pointer_watcher.h
index 8270683214e99f946e0629d433a31662fb71d3a0..715ec130193bc51707283caa7f7247ab90549e6e 100644
--- a/ui/views/pointer_watcher.h
+++ b/ui/views/pointer_watcher.h
@@ -27,6 +27,8 @@ class Widget;
 // NOTE: On mus this allows observation of events outside of windows owned
 // by the current process, in which case the |target| will be null. On mus
 // event.target() is always null.
+// NOTE: Mouse capture change events are sent through OnPointerEventObserved and
+// its |target| is always null.
 class VIEWS_EXPORT PointerWatcher {
  public:
   PointerWatcher() {}
@@ -35,10 +37,6 @@ class VIEWS_EXPORT PointerWatcher {
                                       const gfx::Point& location_in_screen,
                                       Widget* target) = 0;
 
-  // PointerWatcher is informed of capture changes as it's common to create a
-  // MouseEvent of type ui::ET_MOUSE_CAPTURE_CHANGED on capture change.
-  virtual void OnMouseCaptureChanged() {}
-
  protected:
   virtual ~PointerWatcher() {}