GitLab

1. Move html out of string resources
2. polymer binding for UI properties most elements.
3. polymer binding for learn more callbacks
4. Move onNext/overlays to arc_terms_of_service for future
   reuse for in session opt-in extension.
5. Use multiple popup overlays with multiple <p> to support
   overlay text with multiple paragragh.
6. Remove skip button as it's no more supported for user.
   Add TODO for clean up.

Not all work is done with this cl. Things need follow up
1. Handle string loading before login.
2. Better handling webview.
3. Terms of service webview loading uses adding class to set
   display: none.
4. Large group of text are still not broken into blocks. 

Bug: 1047807
Test: Update browser tests
Test: Manual
Change-Id: If627f6680d416a134aa429359fb7352fe0cc5de3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2081252Reviewed-by: Denis Kuznetsov [CET] <antrim@chromium.org>
Commit-Queue: Long Cheng <lgcheng@google.com>
Cr-Commit-Position: refs/heads/master@{#748536}