GitLab

Exposes PDF thumbnailer to misc API. Uses it to fetch PNG bytes for
a local PDF file. Alters MakeThumbnailDataUrlOnThreadPool to accept
base::StringPiece. This allows the existing code path for drivefs
thumbnails and the new code path to re-use it.

Bug: 903742
Change-Id: I561d734a4d168c0ed96118decddab992d67889e2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2291914
Commit-Queue: Bo Majewski <majewski@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#803765}