Suppress TSAN races with net::(anonymous namespace)::g_network_change_notifier

These races have been around 8+ years so new CLs triggering these TSAN failures
should be ignored.  I've prototyped a fix to avoid the races.
This global variable is set very early in Chrome startup and cleared very late
in Chrome shutdown so reads shouldn't race writes.

Bug: 927330
Change-Id: Ic3ed2446e4cee92dbeda83a0b10ad99a1fbf5d63
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1566824
Reviewed-by: Jonathan Metzman <metzman@chromium.org>
Commit-Queue: Paul Jensen <pauljensen@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#650846}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 433cfc173e369a5f51afcd6ef14cab8dbdf9c481

sanitizers/tsan_suppressions.cc

@@ -204,6 +204,9 @@ char kTSanDefaultSuppressions[] =
     // http://crbug.com/797998
     "race:content::SandboxIPCHandler::HandleLocaltime\n"
 
+    // http://crbug.com/927330
+    "race:net::(anonymous namespace)::g_network_change_notifier\n"
+
     // End of suppressions.
     ;  // Please keep this semicolon.