Ongoing in CL https://chromium-review.googlesource.com/c/chromium/src/+/1407012

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/09deb66290457e5653b69e995a884100852ae6f6

commit 09deb66290457e5653b69e995a884100852ae6f6
Author: Antonio Gomes <tonikitoo@igalia.com>
Date: Wed Jan 16 02:52:35 2019

Port current clients of UbertokenFetcher away from PO2TS

This CL is the last out of 4 CLs to incorporate UbertokenFetcher into
the IdentityManager API.

TL;DR: CL allows us to get rid of the PO2TS references from
GaiaWebAuthFlow and ArcAuthContext by making UbertokenFetcher available
through IdentityManager API.

In details, the CL:

1) Introduces an UbertokenFetcher base class to
//components/signin/core/browser, compiled as part of the "shared"
GN target.
The class is very simple, and used mainly to expose UbertokenFetcher
through an IdetntiyManager API.

2) Adds an entry point API IdentityManager::CreateUbertokenFetcher()
that returns an instance of UbertokenFetcherImpl (actually for clients
of this API see the return as an UbertokenFetcher object).

4) Changes the two client-side consumers of the previous UbertokenFetcher
implementation to indirectly instantiate UbertokenFetcherImpl obtained
via IdentityManager::CreateUbertokenFetcher.

BUG= 905243 , 906025 

Change-Id: I419b8af26485ab94c5efdcdefd7fd18ce48c8a8e
Reviewed-on: https://chromium-review.googlesource.com/c/1407012
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Reviewed-by: Yury Khmel <khmel@chromium.org>
Reviewed-by: David Roger <droger@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#623071}
[modify] https://crrev.com/09deb66290457e5653b69e995a884100852ae6f6/chrome/browser/chromeos/arc/auth/arc_auth_context.cc
[modify] https://crrev.com/09deb66290457e5653b69e995a884100852ae6f6/chrome/browser/chromeos/arc/auth/arc_auth_context.h
[modify] https://crrev.com/09deb66290457e5653b69e995a884100852ae6f6/chrome/browser/extensions/api/identity/gaia_web_auth_flow.cc
[modify] https://crrev.com/09deb66290457e5653b69e995a884100852ae6f6/chrome/browser/extensions/api/identity/gaia_web_auth_flow.h
[modify] https://crrev.com/09deb66290457e5653b69e995a884100852ae6f6/components/signin/core/browser/BUILD.gn
[add] https://crrev.com/09deb66290457e5653b69e995a884100852ae6f6/components/signin/core/browser/ubertoken_fetcher.cc
[add] https://crrev.com/09deb66290457e5653b69e995a884100852ae6f6/components/signin/core/browser/ubertoken_fetcher.h
[modify] https://crrev.com/09deb66290457e5653b69e995a884100852ae6f6/components/signin/core/browser/ubertoken_fetcher_impl.h
[modify] https://crrev.com/09deb66290457e5653b69e995a884100852ae6f6/services/identity/public/cpp/DEPS
[modify] https://crrev.com/09deb66290457e5653b69e995a884100852ae6f6/services/identity/public/cpp/identity_manager.cc
[modify] https://crrev.com/09deb66290457e5653b69e995a884100852ae6f6/services/identity/public/cpp/identity_manager.h

 Issue 920209  has been merged into this issue.