Bug 1193062 - Give synthesized NSEvents a timestamp that is in the right space. r=smichaud

NSEvent timestamps are relative to the system start time, not to the reference date.

--HG--
extra : commitid : shDNTICmQP
extra : rebase_source : 2f45dc0e8acc83d5c7379554dfdd6090af694c89
extra : histedit_source : 75add13c0cbcafdafb14e052edea67bd4a0317e2

widget/cocoa/nsChildView.mm

@@ -1127,7 +1127,7 @@ nsresult nsChildView::SynthesizeNativeMouseEvent(LayoutDeviceIntPoint aPoint,
   NSEvent* event = [NSEvent mouseEventWithType:(NSEventType)aNativeMessage
                                       location:windowPoint
                                  modifierFlags:aModifierFlags
-                                     timestamp:[NSDate timeIntervalSinceReferenceDate]
+                                     timestamp:[[NSProcessInfo processInfo] systemUptime]
                                   windowNumber:[[mView window] windowNumber]
                                        context:nil
                                    eventNumber:0