Rename isolate_dependency_tracked to files.

That's the new name, and the next swarming_client roll will refuse the old name.

R=jshin@chromium.org
BUG=

Review URL: https://codereview.chromium.org/607413006

git-svn-id: https://src.chromium.org/chrome/trunk/deps/third_party/icu52@292317 4ff67af0-8c30-449e-8e8b-ad334ec8d88c