Revert "Reland "[blink] Control ScriptStreamer with ScriptResource""

This reverts commit dd9df78ccc1e1ac79a5657966a264562c6d03fb7.

Reason for revert: Makes VR tests flaky (https://crbug.com/894796)

Original change's description:
> Reland "[blink] Control ScriptStreamer with ScriptResource"
> 
> This is a reland of 7bd9163502462762e58d8010577dbf36aeef6c13
> 
> No changes from the original, revert reason is fixed with
> https://chromium-review.googlesource.com/c/1283037
> 
> Original change's description:
> > [blink] Control ScriptStreamer with ScriptResource
> >
> > Move the ScriptStreamer control logic from ClassicPendingScript to
> > ScriptResource. In the future, this will allow us to start streaming
> > a ScriptResource before the ClassicPendingScript is available, e.g on
> > preload.
> >
> > The ClassicPendingScript now only sends one "finished" callback, from
> > ScriptResource. This callback is either when the streaming completes,
> > or when there is no streaming and the ClassicPendingScript has told
> > the ScriptResource that it doesn't intend to start streaming. In the
> > long run, we want all scripts to go through the streaming interface,
> > and we want ScriptResource to control when streaming starts, so the
> > "no more streaming" call will disappear -- however it is necessary to
> > maintain the current behaviour, and be able to control it with a
> > runtime flag.
> >
> > Bug: chromium:865098
> > Change-Id: I2c4cc16635a6538b7ff24a24463fe6f34efd8a2e
> > Reviewed-on: https://chromium-review.googlesource.com/c/1181430
> > Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> > Reviewed-by: Hiroshige Hayashizaki <hiroshige@chromium.org>
> > Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
> > Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#599148}
> 
> TBR=kouhei@chromium.org,kinuko@chromium.org
> 
> Bug: chromium:865098
> Change-Id: I0df324ef8e284f4d3d55a1721d71be5a66a3285c
> Reviewed-on: https://chromium-review.googlesource.com/c/1286450
> Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> Reviewed-by: Hiroshige Hayashizaki <hiroshige@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#601143}

TBR=kinuko@chromium.org,rmcilroy@chromium.org,haraken@chromium.org,hiroshige@chromium.org,kouhei@chromium.org,vogelheim@chromium.org,leszeks@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: chromium:865098
Change-Id: Ibdbd7e80d0fcfacc84a73e83d165581c7f1d02d2
Reviewed-on: https://chromium-review.googlesource.com/c/1297138
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#602310}
20 files changed