RenderFrameImpl: do not retrieve PreviewsState from request

Instead, we can save previews state to InternalDocumentStateData,
similarly to EffectiveConnectionType, and read it from there when
needed. This allows to remove WebDocumentLoader::GetRequest, which
will not be needed soon (see doc linked from a bug).

Bug: 855189
Change-Id: I1f8324685db86e2112b7e2537c2d8602919edb07
Reviewed-on: https://chromium-review.googlesource.com/c/1389121
Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#620542}
3 files changed