Reupload "Add end-to-end browser tests for PluginVm setup flow"

Initial CL: https://chromium-review.googlesource.com/c/chromium/src/+/1494881

Update compared to the reverted CL: Fixed tests.

Adds end-to-end setup flow browser tests.
This CL also adds DCHECKs that check that UI related calls made in the
UI thread.

Test: browser_tests --gtest_filter="PluginVm*"
Bug: 920988
Change-Id: I7b31d141925622a29f984f5b9c7e48c7fe751404
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1499568
Reviewed-by: Igor <igorcov@chromium.org>
Commit-Queue: Olya Kalitova <okalitova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#637682}
3 files changed