Do not assert for blocking call allowed in Thread::Join. We do not allow blocking call from the worker thread, but on Android the worker thread may stop/join a SignalThread, which hits the assert. AssertBlockingIsAllowedOnCurrentThread is used to make sure a thread does not do Invoke, so check that in Thread::Join does not seem to add much value.
Do not assert for blocking call allowed in Thread::Join.
We do not allow blocking call from the worker thread, but on Android the worker thread may stop/join a SignalThread, which hits the assert.
AssertBlockingIsAllowedOnCurrentThread is used to make sure a thread does not do Invoke, so check that in Thread::Join does not seem to add much value.

BUG=3857
R=juberti@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/24709004

Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 1fd362c31ee66283433b60fb5b85f548e8599982

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