Remove ThreadLocalEventNames

This CL removes the ThreadLocalEventNames class and moves all callers over to
using thread-safe strings. I've left ThreadLocalEventNames.h in place because
many files use it to pull in headers. I'll remove it in a future CL.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/26890003

git-svn-id: svn://svn.chromium.org/blink/trunk@159480 bbb929c8-8fbe-4397-9dbb-9b2b20218538