Files.app: Fix progress bar animation for delete operation.

Previously the progress bars for delete operations do not start 0% because
progress value of BEGIN event is not specified.

In addition it is displayed in a moment at start before the correct value is set.

This CL fixes these two problems.

BUG=325607
TEST=start delete operation, observe its progress bar.

Review URL: https://codereview.chromium.org/101813003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238909 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238909