Remove ReadableStreamOperations use from BodyStreamBuffer

Replace use of ReadableStreamOperations in BodyStreamBuffer with
ReadableStream. This CL doesn't change the behavior.

Bug: 894357, 888165, 902633

Change-Id: Icd478dcc59ca86e020d540229d69f0c61fb689c0
Reviewed-on: https://chromium-review.googlesource.com/c/1319408
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Adam Rice <ricea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606775}
13 files changed