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* Update both CastRunner and WebRunner to use the fuchsia.web API.
* Move LegacyMessagePortBridge to be shared between WebEngine and
  CastRunner as the cast API still uses the chromium.web.MessagePort
  API. This API is being transitioned separately.

Bug: 946732
Change-Id: Ic47af0b7b6d6df2599a37f8b2dadf0a63ea8c57c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1560316
Commit-Queue: Fabrice de Gans-Riberi <fdegans@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#651375}