Remove OnDataAvailable() notification when trailers are to be delivered

This CL used the change that is suggested by mpw@ in
https://bugs.chromium.org/p/chromium/issues/detail?id=652935#c1.

Specifically, this CL removes
QuicChromiumClientStream::Delegate::OnDataAvailable()
notification if there is no byte can be read and trailers are to be delivered.

This CL adjusted unit tests to test the correct ordering of events.

BUG=652935

Review-Url: https://codereview.chromium.org/2393233002
Cr-Commit-Position: refs/heads/master@{#423357}
6 files changed