Immediately shut down the instance when creating a pipe fails

Previously, ArcSession reported GENERIC_BOOT_FAILURE to its observer,
but it didn't immediately shut down the container. This CL fixes the
issue.

BUG=chromium:737148
TEST=ARC++ still starts

Change-Id: I8dce70a91c521909406594ac325e84765ee0cb7a
Reviewed-on: https://chromium-review.googlesource.com/579167Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Commit-Queue: Yusuke Sato <yusukes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488515}

components/arc/arc_session.cc

@@ -514,7 +514,7 @@ void ArcSessionImpl::OnInstanceStarted(
   // Stop().
   base::ScopedFD cancel_fd;
   if (!CreatePipe(&cancel_fd, &accept_cancel_pipe_)) {
-    OnStopped(ArcStopReason::GENERIC_BOOT_FAILURE);
+    StopArcInstance();
     return;
   }