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* Fix a bug in MuxingSignalStrategy such that it keeps waiting for both
  strategies to connect instead of giving up and using whatever is
  available. This essentially rewrites the state transition logic.
* Add unittest for MuxingSignalStrategy.

Bug: 966632
Change-Id: Ic94b1ef47b5109acd5d603f02cb8659353c02a82
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1628130
Commit-Queue: Joe Downing <joedow@chromium.org>
Reviewed-by: Joe Downing <joedow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662874}