Bug 1419362 part 5: Clobber required for accessibility IDL changes. r=MarcoZ

As discovered in bug 1419814, changes to accessibility IDL files unfortunately aren't correctly handled by the build system.
Thus, we need a clobber to avoid build failures.

MozReview-Commit-ID: FQeUdWcESI7

--HG--
extra : rebase_source : 471f2985f2b8a4abf45d1c7b826b8a825438965f

CLOBBER

@@ -22,4 +22,4 @@
 # changes to stick? As of bug 928195, this shouldn't be necessary! Please
 # don't change CLOBBER for WebIDL changes any more.
 
-Bug 1419814 - a11y IDL changes causing build failures
+Bug 1419362 - a11y IDL changes not correctly handled by build system