Disable WebUSB client impl
Disable WebUSB client impl

Seeing if this resolves some blink test flake which
appeared recently.

BUG=524248
TBR=jam@chromium.org,reillyg@chromium.org
R=tandrii@chromium.org

Review URL: https://codereview.chromium.org/1308273006

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#345415}

Chilledheart/chromium,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium,Chilledheart/chromium,Chilledheart/chromium,Chilledheart/chromium,axinging/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium,Chilledheart/chromium,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium