port 09de997b (r30442).

original commit message:

    This adds a new ToString runtime function and a fast-path ToStringStub
    (which is just a simple dispatcher for existing functionality), and also
    implements %_ToName using the ToStringStub.

R=weiliang.lin@intel.com
BUG=

Review URL: https://codereview.chromium.org/1326473002

Cr-Commit-Position: refs/heads/master@{#30460}