Don't synthesize mousemove events if the mouse cursor is not on the widget

ui/views/widget/widget.cc

Index: ui/views/widget/widget.cc
diff --git a/ui/views/widget/widget.cc b/ui/views/widget/widget.cc
index 280969a84e5e7d0067d1f10378dec9d6d15061fb..c02d4ed2b25808ab5c3c3140d62ca87b39e51cf5 100644
--- a/ui/views/widget/widget.cc
+++ b/ui/views/widget/widget.cc
@@ -169,6 +169,7 @@ Widget::Widget()
       is_top_level_(false),
       native_widget_initialized_(false),
       native_widget_destroyed_(false),
+      is_mouse_on_widget_(false),
       is_mouse_button_pressed_(false),
       ignore_capture_loss_(false),
       last_mouse_event_was_move_(false),
@@ -988,6 +989,9 @@ gfx::Rect Widget::GetWorkAreaBoundsInScreen() const {
 }
 
 void Widget::SynthesizeMouseMoveEvent() {
+  if (!is_mouse_on_widget_)
+    return;
+
   last_mouse_event_was_move_ = false;
   ui::MouseEvent mouse_event(ui::ET_MOUSE_MOVED, last_mouse_event_position_,
                              last_mouse_event_position_, ui::EventTimeForNow(),
@@ -1230,7 +1234,12 @@ void Widget::OnMouseEvent(ui::MouseEvent* event) {
       }
       return;
 
+    case ui::ET_MOUSE_ENTERED:
+      is_mouse_on_widget_ = true;
+      return;
+
     case ui::ET_MOUSE_EXITED:
+      is_mouse_on_widget_ = false;

[sky, 2015/08/20 18:03:12]

I'm worried we won't always get here. Say you click hold and drag, or we trigger
a nested message loop or other weird cases.
Here's a though, why do we cache the mouse location for
SynthesizeMouseMoveEvent. Why don't we query for the current mouse location in
SynthesizeMouseMoveEvent, that way you can detect if mouse is over widget or
not.

[oshima, 2015/08/21 01:00:15]

For drag case, the mouse location is outside of the widget, so this still should
work correctly. I think the nested message loop case won't affect this, although
I may be missing something.
This should work too, I think.

       last_mouse_event_was_move_ = false;
       if (root_view)
         root_view->OnMouseExited(*event);