Return after reposting BrowserChildProcessHostImpl::OnMojoError() on the right thread

BUG=667280

Review-Url: https://codereview.chromium.org/2522453002
Cr-Commit-Position: refs/heads/master@{#433546}
diff --git a/content/browser/browser_child_process_host_impl.cc b/content/browser/browser_child_process_host_impl.cc
index c9111f1..c786b11 100644
--- a/content/browser/browser_child_process_host_impl.cc
+++ b/content/browser/browser_child_process_host_impl.cc
@@ -585,6 +585,7 @@
     task_runner->PostTask(
         FROM_HERE, base::Bind(&BrowserChildProcessHostImpl::OnMojoError,
                               process, task_runner, error));
+    return;
   }
   if (!process)
     return;