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This updates the Media Router integration tests so they run in the
Chromium waterfall with the open source Media Router component
extension and its mock (test) Media Route Provider.

Additional changes:

- Removes extension from top level BUILD.gn as it is only used for
  browser tests at the moment.
- Splits the targets for Media Router browser tests into integration tests
  (part of main browser_tests suite), e2e tests (which require the
  external component extension), perf tests, and shared support code.
- Renames the "test" extension to the "telemetry" extension used for perf
  tests to avoid confusion.
- Updates README files
- One test is not compatible with the Chromium component and need
  to be fixed.  Bugs 818767 filed for follow-up.

Bug: 698796
Change-Id: I6cc9302ffd72de95630ce33ca3617b3b73b9e722
Reviewed-on: https://chromium-review.googlesource.com/917214
Commit-Queue: mark a. foltz <mfoltz@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Derek Cheng <imcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543005}