Bug 1289500 - Don't load GTK IM module on content process. r=masayuki

Now content sandbox process is enabled.  Since uim-mozc uses vfork, it causes sandbox violation.  It is unnecessary to load IM module on content process becasue we don't use GTK IM APIs on content process.

MozReview-Commit-ID: GrPlmazzEMd

--HG--
extra : rebase_source : e12ec563807627a7fb84b2ca56eaa552aac22643

ipc/glue/GeckoChildProcessHost.cpp

@@ -730,6 +730,14 @@ GeckoChildProcessHost::PerformAsyncLaunchInternal(std::vector<std::string>& aExt
   if (privs == base::PRIVILEGES_DEFAULT) {
     privs = DefaultChildPrivileges();
   }
+
+#if defined(MOZ_WIDGET_GTK)
+  if (mProcessType == GeckoProcessType_Content) {
+    // disable IM module to avoid sandbox violation
+    newEnvVars["GTK_IM_MODULE"] = "gtk-im-context-simple";
+  }
+#endif
+
   // XPCOM may not be initialized in some subprocesses.  We don't want
   // to initialize XPCOM just for the directory service, especially
   // since LD_LIBRARY_PATH is already set correctly in subprocesses