Bug 1268544: Followup: fix missing include in DocAccessibleChildBase; r=me

MozReview-Commit-ID: CzeTjJa9gg6

--HG--
extra : rebase_source : 93827e6cac5acf3df06147de28452293fc0befe6

accessible/ipc/DocAccessibleChildBase.cpp

@@ -5,6 +5,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "mozilla/a11y/DocAccessibleChildBase.h"
+#include "mozilla/a11y/ProxyAccessibleBase.h"
 
 #include "Accessible-inl.h"