[Signin] Add feature flag for Menagerie API migration

This CL adds a feature flag for the legacty Menagerie API migration.
Menagerie is used to fetch profile data(names, avatar) on Android.

Bug: 1136452
Change-Id: I6c6faef5eef8a67be2cf7ed51ecc24b822df701a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2673830
Reviewed-by: Mihai Sardarescu <[email protected]>
Commit-Queue: Alice Wang <[email protected]>
Cr-Commit-Position: refs/heads/master@{#856284}
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index ac8705c..2cb3596 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -94,6 +94,11 @@
     "Synchronizes uninstallation of default Chrome apps across Chrome OS "
     "devices.";
 
+const char kDeprecateMenagerieAPIName[] = "Deprecate Menagerie API on Android";
+const char kDeprecateMenagerieAPIDescription[] =
+    "If enabled, the legacy Menagerie API for profile data will be replaced by "
+    "the new profile data source";
+
 const char kDetectedSourceLanguageOptionName[] =
     "Use Detected Language string on Desktop and Android";
 const char kDetectedSourceLanguageOptionDescription[] =