Bug 1266298 - Add sys_fchmod to seccomp whitelist r=jld

MozReview-Commit-ID: 4kFgfxhCMFl

--HG--
extra : transplant_source : h%D1%90%ACfP%DC%5C%CB%CC%84%CE%B7%40%17%14%B1%10%FC%AA

security/sandbox/linux/SandboxFilter.cpp

@@ -514,6 +514,7 @@ public:
     case __NR_utimes:
     case __NR_unlink:
     case __NR_fchown:
+    case __NR_fchmod:
 #endif
       return Allow();