Associate a bug with network service failing test ProxySettingsApiTest.ProxyEventsParseError.

Bug: 851609
Cq-Include-Trybots: luci.chromium.try:linux_mojo
Change-Id: I2f261550d21f80e4b2143c0253a3867f11091885
Reviewed-on: https://chromium-review.googlesource.com/1175054
Commit-Queue: Eric Roman <eroman@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583054}

testing/buildbot/filters/mojo.fyi.network_browser_tests.filter

@@ -119,9 +119,9 @@
 -ResourceLoadingHintsBrowserTest.ResourceLoadingHintsHttp
 -ResourceLoadingHintsBrowserTest.ResourceLoadingHintsHttpsNoWhitelisted
 
-# These rely on proxy configuration and PAC execution being configured on the
-# legacy in-process URLRequestContext. They should be removed or updated to
-# use Mojo APIs instead.
+# https://crbug.com/851609
+# Extension listeners for "chrome.proxy.onProxyError" are not called for errors
+# in PAC scripts.
 -ProxySettingsApiTest.ProxyEventsParseError
 
 # http://crbug.com/827582