Navi: Create onboarding groups that are allowed to ping finch.

Only users in a group will be able to ping finch to make retention
analysis easier.

Groups are:
  - Specified by finch
  - Incremented with each new version
  - Not reused
  - Cleared out when experiment ends

Bug: 904051
Change-Id: I726b43cd122969447cd6d2e3e207b12a5e9c97b4
Reviewed-on: https://chromium-review.googlesource.com/c/1330899
Reviewed-by: Dominic Battré <[email protected]>
Reviewed-by: Stefan Kuhne <[email protected]>
Reviewed-by: Tommy Martino <[email protected]>
Reviewed-by: Scott Chen <[email protected]>
Commit-Queue: Hector Carmona <[email protected]>
Cr-Commit-Position: refs/heads/master@{#609403}
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index c9986a1..edd85e91 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -381,6 +381,7 @@
 // Deprecated 11/2018.
 const char kNetworkQualities[] = "net.network_qualities";
 const char kForceSessionSync[] = "settings.history_recorded";
+const char kOnboardDuringNUX[] = "browser.onboard_during_nux";
 
 // Register prefs used only for migration (clearing or moving to a new key).
 void RegisterProfilePrefsForMigration(
@@ -410,6 +411,7 @@
 
   registry->RegisterDictionaryPref(kNetworkQualities, PrefRegistry::LOSSY_PREF);
   registry->RegisterBooleanPref(kForceSessionSync, false);
+  registry->RegisterBooleanPref(kOnboardDuringNUX, false);
 }
 
 }  // namespace
@@ -873,4 +875,5 @@
   // Added 11/2018.
   profile_prefs->ClearPref(kNetworkQualities);
   profile_prefs->ClearPref(kForceSessionSync);
+  profile_prefs->ClearPref(kOnboardDuringNUX);
 }