Bug 977559 - PointerId we can get from system. r=mbrubeck,smaug

widget/windows/winrt/MetroInput.cpp

@@ -488,6 +488,7 @@ MetroInput::OnPointerNonTouch(UI::Input::IPointerPoint* aPoint) {
                          WidgetMouseEvent::eReal,
                          WidgetMouseEvent::eNormal);
   event->button = button;
+  aPoint->get_PointerId(&event->pointerId);
   InitGeckoMouseEventFromPointerPoint(event, aPoint);
   DispatchAsyncEventIgnoreStatus(event);
 }