Introduce blink::ReadableStream

Introduce blink::ReadableStream which is a ScriptWrappable. This CL
doesn't change the behavior because the interface is not (yet) exposed.

Bug: 894357, 888165, 902633
Change-Id: Ie0f14e0efcc7d48034fff8317ba7f70f3f8ecd3b
Reviewed-on: https://chromium-review.googlesource.com/c/1319222
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Adam Rice <ricea@chromium.org>
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606749}
10 files changed