Fix test harness for Test262 to not use symlinks.
Fix test harness for Test262 to not use symlinks.

This is necessary for the --download-data option to work on Windows
where we do not have symlinks available. Note that we still have no
automatic way of bumping the existing Test262 revision without deleting
the data directory manually.

R=jkummerow@chromium.org
TEST=test262

Review URL: https://chromiumcodereview.appspot.com/9866046

git-svn-id: b158db1e4b4ab85d4c9e510fdef4b1e8c614b15b@11172 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh