Reduce unnecessary #includes to speed up compilation. r=bryner/sfraser sr=alecf b=64023

widget/src/mac/nsMenuBar.h

@@ -27,6 +27,7 @@
 #include "nsIMenuListener.h"
 #include "nsIDocumentObserver.h"
 #include "nsIChangeManager.h"
+#include "nsIPresContext.h"
 #include "nsSupportsArray.h"
 #include "nsVoidArray.h"
 #include "nsHashtable.h"