This bug is free to take now; see the solution to the DeviceO2TS issue in  crbug.com/907540 .

Taking this

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/97ba8f05f634628e04a09a196a3ae82a1e7d2131

commit 97ba8f05f634628e04a09a196a3ae82a1e7d2131
Author: Sergio Villar Senin <svillar@igalia.com>
Date: Tue Jan 15 11:37:19 2019

Convert IdentityGetAuthTokenFunction from using PO2TS to IdentityManager

The ProfileOAuth2TokenService was used for several things from
checking the availability of refresh tokens for a given account to
starting access token requests. In order to completely migrate it to
IdentityManager a new API had to be added to both IdentityManager and
AccountTokenFetcher since it was not possible to request an access
token by passing a client id and secret.

Last but not least, the identity_manager_ attribute was renamed to
mojo_identity_manager_.

Bug:  910202 ,  910203 
Change-Id: I97de7156c8901de4a566b0133448c2d83cd4b37c
Reviewed-on: https://chromium-review.googlesource.com/c/1370279
Commit-Queue: Sergio Villar <svillar@igalia.com>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622815}
[modify] https://crrev.com/97ba8f05f634628e04a09a196a3ae82a1e7d2131/chrome/browser/extensions/api/identity/identity_apitest.cc
[modify] https://crrev.com/97ba8f05f634628e04a09a196a3ae82a1e7d2131/chrome/browser/extensions/api/identity/identity_get_auth_token_function.cc
[modify] https://crrev.com/97ba8f05f634628e04a09a196a3ae82a1e7d2131/chrome/browser/extensions/api/identity/identity_get_auth_token_function.h
[modify] https://crrev.com/97ba8f05f634628e04a09a196a3ae82a1e7d2131/services/identity/public/cpp/access_token_fetcher.cc
[modify] https://crrev.com/97ba8f05f634628e04a09a196a3ae82a1e7d2131/services/identity/public/cpp/access_token_fetcher.h
[modify] https://crrev.com/97ba8f05f634628e04a09a196a3ae82a1e7d2131/services/identity/public/cpp/identity_manager.cc
[modify] https://crrev.com/97ba8f05f634628e04a09a196a3ae82a1e7d2131/services/identity/public/cpp/identity_manager.h