Currently the WebUIPolymer2 feature flag affects which Polymer version is used across all WebUI pages.

In order to move the migration forward, we need finer granularity, so that we cun turn on Polymer 2 on some pages, but not others (like OOBE).

Specifically a next milestone for the overall migration would be the following?

- All of Desktop using Polymer 2 (already planned for M72).
- All of ChromeOS, except OOBE using Polymer 2

This will allow turning on Polymer 2 for ChromeOS on Canary/Dev so that these pages can be tested by QA.