manifest: rework icon selector to include small icon cut-off
Up until this point, arbitarily small icons have been selected as being suitable
for download.
We no longer want to do this as it can lead to pixellated looking icons which
look quite ugly. Instead we impose a cutoff similar to Android icon selection -
we stop allowing icons which are smaller than one density bucket below the bucket
of the device.
The tests have been changed to reflect this fact as they were also allowing small
icons.
BUG=513666
Review URL: https://codereview.chromium.org/1285063003
Cr-Commit-Position: refs/heads/master@{#344759}
8 files changed
