Revert "Revert "Downloads: detect failed file icons and show default thumbnail""

This reverts commit 14d25fb9050e3a5b9eea892514325e7a44d9e894.

This is a roll-forward with a fix to the URL of an iconset to load
(see the diff between patchsets 1 and 2).

NOPRESUBMIT=true  # existing issue in destination.js

Bug: 855259, 912678
Change-Id: I3aeb26263de682ecb2f0596e336ec20ab5c19807
Reviewed-on: https://chromium-review.googlesource.com/c/1371079
Commit-Queue: Dan Beam <dbeam@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615412}
17 files changed