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This CL creates a feature-policy directory under wpt/, as well, provides some
framework for testing features with feature policy.

Using the framework, this CL added feature policy tests for payment, and
modified existing feature policy usb tests using the framework introduced.

Bug: 732003
Change-Id: I7d690acfe70b63d4935f6a4c6c43e94da5503827
Reviewed-on: https://chromium-review.googlesource.com/533953Reviewed-by: Ian Clelland <iclelland@chromium.org>
Commit-Queue: Luna Lu <loonybear@chromium.org>
Cr-Commit-Position: refs/heads/master@{#481008}