Update polymer_browser_test_base to use source absolute paths.

Source absolute paths are now supported, so re-writing all paths
in terms of the ROOT_PATH is now unnecessary complexity.

All subclasses of PolymerTest will have this complexity removed
in a follow-up CL.

Change-Id: Id3106bcae11812b34cf2d2deba9fc2ed01722778
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1581344
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: A Olsen <olsen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653944}
1 file changed