[Messages] Add flags for infrastructure and passwords infobars

This CL adds feature flags and about:flags entries for a couple of
flags:
- MessagesForAndroidInfrastructure will control initialization of
  infrastructure classes (MessageQueueManager, etc.)
- MessagesForAndroidPasswordsName will control whether save/update
  password uses Infobars or Messages UI.

BUG=1123947
[email protected]

Change-Id: I4b3e3920d2909f8e6144cc197d8fddc029356f86
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2388949
Reviewed-by: Lijin Shen <[email protected]>
Reviewed-by: Theresa  <[email protected]>
Commit-Queue: Pavel Yatsuk <[email protected]>
Cr-Commit-Position: refs/heads/master@{#804317}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index e223f68..3cb15683 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1648,6 +1648,12 @@
 extern const char kInterestFeedFeedbackName[];
 extern const char kInterestFeedFeedbackDescription[];
 
+extern const char kMessagesForAndroidInfrastructureName[];
+extern const char kMessagesForAndroidInfrastructureDescription[];
+
+extern const char kMessagesForAndroidPasswordsName[];
+extern const char kMessagesForAndroidPasswordsDescription[];
+
 extern const char kOfflineIndicatorAlwaysHttpProbeName[];
 extern const char kOfflineIndicatorAlwaysHttpProbeDescription[];