The TickTimer is incremented on each call to GetAudioInternal(). Other
than that, the new object is not used yet.
Also adding a unit test in NetEqImplTest to verify that the tick timer
is incremented in the call to NetEq::GetAudio.
BUG=webrtc:5608
Review URL: https://codereview.webrtc.org/1903153005
Cr-Commit-Position: refs/heads/master@{#12493}