diagnose_bloat.py: Suppress warning for downloads.

A recent gsutil update added a warning about download speeds. Instead
of trying to filter out the warning we use "gsutil stat" to get the
download size.

Bug: 
Change-Id: Ie614aff2d2d04a81cc1dde47c5d6a71f0cfbd34e
Reviewed-on: https://chromium-review.googlesource.com/841182
Reviewed-by: Peter Wen <[email protected]>
Commit-Queue: Eric Stevenson <[email protected]>
Cr-Commit-Position: refs/heads/master@{#525827}
1 file changed