GitLab

* Add stream request support to ProtobufHttpStatus, which includes some
  refactoring in the code.
* Make ProtobufHttpClient directly own the requests, to make lifetime
  managing less painful.

Bug: 1103416
Change-Id: I9c1f62acb4e02cd968387bc4cc34db8dd6268c25
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2299536
Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Reviewed-by: Joe Downing <joedow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#790112}