Port 09de997b

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=bmeurer@chromium.org, jyan@ca.ibm.com, dstence@us.ibm.com, joransiu@ca.ibm.com
BUG=v8:4307
LOG=n

Review URL: https://codereview.chromium.org/1310493004

Cr-Commit-Position: refs/heads/master@{#30449}