GitLab

- Migrate inline login flow to use Polymer.
- Remove unused method: "handleOAuth2TokenFailure"
- Remove "show-back-button" call, and use <if expr="chromeos"> to show
the button on ChromeOS only.

Bug: 1096007
Test: browser_tests --gtest_filter="*InlineLoginBrowserTest*"
Change-Id: If146b080bb0fef65f8e931ac35809a8dfa8aa66b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2279795Reviewed-by: Yusuf Sengul <yusufsn@google.com>
Reviewed-by: Kush Sinha <sinhak@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: James MacLean <wjmaclean@chromium.org>
Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Commit-Queue: Anastasiia N <anastasiian@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791531}