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There seems to be a race on whether the count of datachannels
is incremented before a session goes to "connected". This CL
allows both 0 and 1.

The test would fail ~1/4000 times on a Linux workstation.

Bug: 771540
Change-Id: Ic250443c2addef995dbb26e7cd021a516dcd023b
Reviewed-on: https://chromium-review.googlesource.com/721379Reviewed-by: Henrik Boström <hbos@chromium.org>
Commit-Queue: Harald Alvestrand <hta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#509564}