[signin] Add metrics to track the source for refresh token updated events

This CL add a source for update and revoke credentials operations. It then
surfaces the source in the chrome://signin-internals page.

This CL also records the following histograms that track refresh token events:
* Signin.RefreshTokenUpdated.ToValidToken.Source
* Signin.RefreshTokenUpdated.ToInvalidToken.Source
* Signin.RefreshTokenRevoked.Source

These histograms are needed to validate the assumptions of how often tokens
are revoked by the browser and the sources for the token revocations.

Bug: 896182

Change-Id: I2fcab80ee8e5699708e695bc3289fa6d34859a90
Reviewed-on: https://chromium-review.googlesource.com/c/1286464
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: David Roger <droger@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Mihai Sardarescu <msarda@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606181}
void PeopleHandler::CloseUI() {
  CloseSyncSetup();
  FireWebUIListener("page-status-changed", base::Value(kDonePageStatus));
}

void PeopleHandler::CloseUI() {
  CloseSyncSetup();
  FireWebUIListener("page-status-changed", base::Value(kDonePageStatus));
}
