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This test moves all the tests from third_party/WebKit/LayoutTests/usb
to third_party/WebKit/LayoutTests/external/wpt/webusb. The WebUSB Test
API polyfill is included in a new resources/chromium directory and
loaded automatically when the tests are run in a Chromium-based browser
with the --enable-blink-features=MojoJS,MojoJSTest flag set.

BUG=705734

Review-Url: https://codereview.chromium.org/2789723003
Cr-Commit-Position: refs/heads/master@{#481732}