Is the expectation that we rewrite our webUI to use polymer2? What's the timeframe in which you're expecting these to be resolved?

The goal is to modify the UI and/or tests so that the tests pass with Polymer 2 enabled. This is an initial step in the process of migrating web UI to use Polymer 2; there may be other issues not caught by automated tests. Migration should not require re-writing the UI, only some (generally small) modifications. See for example https://crrev.com/c/1162266, which fixed some print preview tests. Some other examples of fixes can be found in many of the CLs attached to https://crbug.com/738611 and https://crbug.com/860069, and general documentation on upgrading from Polymer 1 to Polymer 2 is at https://www.polymer-project.org/2.0/docs/upgrade. 

For timing, we are currently targeting M-71.

@mfoltz: Trying to determine whether it is worth investing time in fixing those tests, given that this UI is going to be replaced soon. Can you share an update on when is the expected removal of this code?

FYI, I had started a CL to fix some of those tests at https://chromium-review.googlesource.com/c/chromium/src/+/1270099.

We are aiming for M71 to ship the Views UI but the WebUI will not be removed until later in Q4.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c58c214d0b93fe57848b5c9b4e09df26b82a910d

commit c58c214d0b93fe57848b5c9b4e09df26b82a910d
Author: rbpotter <rbpotter@chromium.org>
Date: Mon Oct 15 23:30:38 2018

Web UI Polymer 2: Fix remaining media_router tests

MediaRouterElementsBrowserTest.MediaRouterContainerCastModeList
MediaRouterElementsBrowserTest.MediaRouterContainerFilterPart1

Bug:  875463 
Change-Id: I6037ea16e264307a801840964197c058f33ab2a5
Reviewed-on: https://chromium-review.googlesource.com/c/1279415
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599775}
[modify] https://crrev.com/c58c214d0b93fe57848b5c9b4e09df26b82a910d/chrome/test/data/webui/media_router/media_router_container_cast_mode_list_tests.js
[modify] https://crrev.com/c58c214d0b93fe57848b5c9b4e09df26b82a910d/chrome/test/data/webui/media_router/media_router_container_filter_tests.js
[modify] https://crrev.com/c58c214d0b93fe57848b5c9b4e09df26b82a910d/chrome/test/data/webui/media_router/media_router_container_test_base.js
[modify] https://crrev.com/c58c214d0b93fe57848b5c9b4e09df26b82a910d/testing/buildbot/filters/webui_polymer2_browser_tests.filter