PDF Viewer Update: Add responsive behavior for embedded viewers

At 500px, hide sidenav, sidenav toggle, and fit button.
At 420px, hide view buttons.
At 200px, hide the entire toolbar.

Fixed: 1119953
Change-Id: I3ffc07203380fc7259c5b162159d340854866b1d
Bug: 1119953
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2393515


Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Commit-Queue: Daniel Hosseinian <dhoss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805627}