Force enable V0 APIs for FilesApp extension w Polymer1.

This patch is a preparation for Shadow DOM V0, Custom Element V0 (CEv0) and HTML Imports removal.
Intent to Deprecate and Remove: http://bit.ly/2RGHe3x
Though we soon make these APIs only available for test by turning the json5 feature flag
from status: "stable" to status: "test", there is browser tests/chrome internal components
that use them.

FilesApp finished migration but it was only for w/o Polymer2.
FilesApp w Polymer1 still needs the APIs for it.
Descussion of flagging was done at previous patch among Jochen and Devlin: crrev.com/c/1405955


Bug: 924873, 911943

Change-Id: I0d3038ce5d21c410e1a055b57752d0df62cf62fb
Reviewed-on: https://chromium-review.googlesource.com/c/1496259
Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: Yoichi Osato <yoichio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636714}
1 file changed