[ MimeHandlerView ] Disable a <webview> permission test with the flag

Frame-based MHV does not respect permissions now. This CL disables the
test to unblock adding a test config and tracks permission support in
its own bug.

TBR=wjmaclean@chromium.org

Bug: 963694
Change-Id: Idcf99cfcd1caa42ed82adda519892c8e97aa7f4f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1615500


Reviewed-by: James MacLean <wjmaclean@chromium.org>
Reviewed-by: Ehsan Karamad <ekaramad@chromium.org>
Commit-Queue: Ehsan Karamad <ekaramad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#660546}