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* Removes CastChannel implementation (it's now provided by Agent).
* Removes QueryableData implementation.
* Removes CastChannel from CastRunner integration tests.
* Add ApiBindings e2e test to CastRunner integration tests.
* Cleans up "metrics" from not implemented stubs.
* Cleans up some transitional code and makes the ApiBindings connection
  mandatory.


Bug: 953958
Change-Id: I28a56131f896c46697369711d3c5e7d0aa72efd4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1656110
Commit-Queue: Kevin Marshall <kmarshall@chromium.org>
Reviewed-by: Fabrice de Gans-Riberi <fdegans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672588}