GitLab

Problem:
When access token request fails with unexpected errors those get
translated to "invalid credentials". In response auth_sync_observer.cc
marks refresh token as invalid which prevents offline auth on next startup.

oauth2_access_token_fetcher_impl.cc:
 - Handle all 5xx http codes as transient errors.
 - Log error for unexpected codes.

profile_sync_service.cc:
 - handle REQUEST_CANCELLED and SERVICE_ERROR as transient error, retry instead of
   notifying observers.
 - Log error for unexpected auth errors.

BUG=394939
R=rogerta@chromium.org,zea@chromium.org

Review URL: https://codereview.chromium.org/472403002

Cr-Commit-Position: refs/heads/master@{#290158}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@290158 0039d316-1c4b-4281-b951-d872f2087c98