Files.app: Let Files.app delay to show the progress bar for delete operation.

Delete operations are usually complete quickly.  So we would not like to show
the progress bar at first.  If the operation takes more than
ProgressCenterHandler.PENDING_TIME_MS_, we adds the item to the progress center.

BUG=277432
TEST=manually
R=yoshiki@chromium.org

Review URL: https://codereview.chromium.org/54413002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232672 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232672