In QUIC, add WriteStatus WRITE_STATUS_BLOCKED_DATA_BUFFERED and use it to represent "A WritePacket caused socket to block and the packet is buffered in writer". Not protected, because this status code is not used in GFE.

This is intended to be used by batch packet writers, for them, whether the
packet that caused write block is buffered can vary from one WritePacket call
to another. The per-class IsWriteBlockedDataBuffered() method is not enough to
express that.

Merge internal change: 228872041

R=rch@chromium.org

Change-Id: I39bdd8f6d1b9e7442f7d51c54231002227790809
Reviewed-on: https://chromium-review.googlesource.com/c/1407030
Reviewed-by: Ryan Hamilton <rch@chromium.org>
Commit-Queue: Bin Wu <wub@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622070}
7 files changed