Create RTCIceTransport using a webrtc::IceTransportInterface object.

Previously, when creating a blink::RTCIceTransport, the corresponding
webrtc::IceTransportInterface object was created by the
IceTransportAdapterImpl. However, in DTLS transport implementation, the
webrtc object is preexisting. Pass the preexisting webrtc object when creating
the blink::RTCIceTransport object in this case.

Bug: 907849
Change-Id: Ia024afc101be830e30f233d6ef1bf39f141227df
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1520486
Commit-Queue: Marina Ciocea <marinaciocea@chromium.org>
Reviewed-by: Harald Alvestrand <hta@chromium.org>
Reviewed-by: Henrik Boström <hbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#642487}
9 files changed