[iOS] Adding user action metrics when signing in

For some reasons, those metrics were not implemented for
sign-in before unity.
  + Signin_Signin_WithDefaultSyncSettings
  + Signin_Signin_WithAdvancedSyncSettings

This patch adds implementations for those 2 metrics for pre-unity
and unity code.

Also "Signin_Undo_Signin" is added for unity code (already implemented)
with pre-unity.

Bug: 937820
Change-Id: I27ec9769e9954b1daeccd273f4d663c35f9fa605
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1496981
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Jérôme Lebel <jlebel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#637585}
1 file changed