Add an about:flags entry for SyncSupportSecondaryAccount

The feature itself was added in
https://chromium-review.googlesource.com/c/chromium/src/+/1162174

Bug: 871221
Cq-Include-Trybots: luci.chromium.try:ios-simulator-cronet;luci.chromium.try:ios-simulator-full-configs
Change-Id: I0cc3527eb25a2e015fa3e6ae458028680f069815
Reviewed-on: https://chromium-review.googlesource.com/1195507
Reviewed-by: Jan Krcal <[email protected]>
Commit-Queue: Marc Treib <[email protected]>
Cr-Commit-Position: refs/heads/master@{#587459}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 1a22915f..542ca41 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1115,6 +1115,9 @@
 extern const char kSyncStandaloneTransportName[];
 extern const char kSyncStandaloneTransportDescription[];
 
+extern const char kSyncSupportSecondaryAccountName[];
+extern const char kSyncSupportSecondaryAccountDescription[];
+
 extern const char kSyncUSSAutofillWalletDataName[];
 extern const char kSyncUSSAutofillWalletDataDescription[];