GOM optimize phase should handle non-SCM files accordingly.

Currently, BaselineOptimizer::_move_baselines() attempts to SCM-delete
files regardless of whether they are under version control, possibly
triggering exceptions.

This CL tracks non-SCM files in a separate list and deletes them using
file system methods.

BUG=334270
R=ojan@chromium.org

Review URL: https://codereview.chromium.org/138733002

git-svn-id: svn://svn.chromium.org/blink/trunk@165225 bbb929c8-8fbe-4397-9dbb-9b2b20218538