Stifle lint warnings about header guards not being present in quic_flags_list.h

Change-Id: I3b76a2332b7a39ccb2c521d72ea908112fea2955
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1504005
Commit-Queue: Zhongyi Shi <zhongyi@chromium.org>
Reviewed-by: Zhongyi Shi <zhongyi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#637945}

net/quic/quic_flags_list.h

@@ -6,6 +6,7 @@
 // inside a macro to generate values. The following line silences a
 // presubmit warning that would otherwise be triggered by this:
 // no-include-guard-because-multiply-included
+// NOLINT(build/header_guard)
 
 // This file contains the list of QUIC protocol flags.