mash: Fix DCHECK when clicking on window close box

mash/wm/frame/move_event_handler.cc

Index: mash/wm/frame/move_event_handler.cc
diff --git a/mash/wm/frame/move_event_handler.cc b/mash/wm/frame/move_event_handler.cc
index 256e0aa88d32b6a18a79fa2acdbf0621d787dcec..0d3e3ca3974243424099ad45da3ae4e49208a408 100644
--- a/mash/wm/frame/move_event_handler.cc
+++ b/mash/wm/frame/move_event_handler.cc
@@ -58,6 +58,12 @@ void MoveEventHandler::ProcessLocatedEvent(ui::LocatedEvent* event) {
   const bool had_move_loop = move_loop_.get() != nullptr;
   DCHECK(event->IsMouseEvent() || event->IsTouchEvent());
 
+  // Non-client buttons like the close box capture the mouse during clicks.
+  // Explicitly ignore those events here instead of below because there is no
+  // PointerEvent equivalent into which the event can be converted.
+  if (event->type() == ui::ET_MOUSE_CAPTURE_CHANGED)

[msw, 2016/03/29 15:47:40]

The PointerEvent ctors will NOTREACHED on other mouse and touch event types that
aren't in those switch statements. Should we guard more broadly against these?
Perhaps we should add a pointer event util/factory function that checks if it
can convert, then return false/null if not?
https://code.google.com/p/chromium/codesearch#chromium/src/ui/events/event.cc...

[James Cook, 2016/03/29 17:38:07]

Yeah, good point.  I talked to Sadrul and we decided to add a util function
PointerEvent::CanConvertFrom(const Event&). I looked at doing a factory
function, but almost all callers of the PointerEvent converters have the event
on the stack, so returning nullptr is awkward, and we don't have an
event-representing-null I can use either.

+    return;
+
   // TODO(moshayedi): no need for this once MoveEventHandler directly receives
   // pointer events.
   scoped_ptr<ui::PointerEvent> pointer_event;