Replace ice_connection_to_client_unittest.cc with connection_unittest.cc

The new tests setup both ends of the connection, which also means
they test both ends. Previously there were no unittests for
ConnectionToHostImpl. It will also be possible to use the same tests
for WebRTC-based connections.

Review URL: https://codereview.chromium.org/1531983002

Cr-Commit-Position: refs/heads/master@{#365948}
9 files changed