QuicChromiumClientStream handle Read() after trailers are received but not yet delivered

This CL changes QuicChromiumClientStream::Read() to return ERR_IO_PENDNG if
trailers are received but not yet delivered. This CL additionally posts a
OnDataAvailable task when trailers are delivered so as to notify delegate of the
FIN flag.

BUG=652935

Review-Url: https://codereview.chromium.org/2405523002
Cr-Commit-Position: refs/heads/master@{#424183}
4 files changed