This reverts commit 7fa071a4.

Reason for revert: https://bugs.chromium.org/p/chromium/issues/detail?id=729482

Original change's description:
> Reland [parser] Refactor streaming scanner streams.
> 
> Unify, simplify logic, reduce UTF8 specific handling.
> 
> Intend of this is also to have stream views.
> Stream views can be used concurrently by multiple threads, but
> only one thread may fetch new data from the underlying source.
> This together with unified stream view creation is intended to be
> used for parse tasks.
> 
> BUG=v8:6093
> 
> Change-Id: I3bce48185fa2c986d16619a9a8ece3ff4c4f5e60
> Reviewed-on: https://chromium-review.googlesource.com/509489
> Reviewed-by: Daniel Vogelheim <vogelheim@chromium.org>
> Reviewed-by: Marja Hölttä <marja@chromium.org>
> Commit-Queue: Wiktor Garbacz <wiktorg@google.com>
> Cr-Commit-Position: refs/heads/master@{#45688}

TBR=marja@chromium.org,vogelheim@chromium.org,wiktorg@google.com
# Not skipping CQ checks because original CL landed > 1 day ago.
BUG=v8:6093

Change-Id: Iefa7c43a2f6ae3a7f3ef0f77d87b6ae36ae4be99
Reviewed-on: https://chromium-review.googlesource.com/525712Reviewed-by: Marja Hölttä <marja@chromium.org>
Reviewed-by: Daniel Vogelheim <vogelheim@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45725}