Add linux_chromium_cfi_rel_ng to list of clang roll tryjobs.

A bot with the same configuration will soon live on chromium.memory,
so we should make sure we don't break it.

Bug: 732652
Change-Id: I7ded28d433691306666912d12eb6f2212a803c65
Reviewed-on: https://chromium-review.googlesource.com/569604
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Peter Collingbourne <pcc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#486426}

docs/updating_clang.md

@@ -30,7 +30,7 @@ $ for x in Linux_x64 Mac Win ; do \
     git cl try -m tryserver.chromium.mac -b mac_chromium_asan_rel_ng &&
     git cl try -m tryserver.chromium.linux -b linux_chromium_chromeos_dbg_ng \
       -b linux_chromium_chromeos_asan_rel_ng -b linux_chromium_msan_rel_ng \
-      -b fuchsia &&
+      -b fuchsia -b linux_chromium_cfi_rel_ng &&
     git cl try -m tryserver.blink -b linux_trusty_blink_rel
 ```
 1.  Commit roll CL from the first step