Files.app: Add a unit test of ProgressCenterHandler class.

This CL adds a unit test of ProgressCenterHanler class for copy operatons.

BUG=324679
TEST=file_manager_jstest
R=yoshiki@chromium.org

Review URL: https://codereview.chromium.org/98363003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238332 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238332