GitLab

 - In the frontend, hardcode the pdf-viewer-update-enabled attribute.
   Previously present/absent based on the state of the flag.
 - In the backend, remove checks for
   base::FeatureList::IsEnabled(features::kPDFViewerUpdate)

As a result of these changes --disable-features=PDFViewerUpdate no
longer works, in the sense that even if specified it will show the
new UI. Newly dead code (old UI) will be removed in follow up CLs.

Bug: 1164004
Change-Id: I0321f2f22e1358c69f6dc5d5c2662739e0b7ead7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2638992
Commit-Queue: dpapad <dpapad@chromium.org>
Reviewed-by: Daniel Hosseinian <dhoss@chromium.org>
Reviewed-by: K. Moon <kmoon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845578}