[runtime] Add %ToString and %_ToString and remove the TO_STRING builtin.

[runtime] Add %ToString and %_ToString and remove the TO_STRING builtin.

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=mstarzinger@chromium.org, yangguo@chromium.org
BUG=v8:4307
LOG=n

Committed: https://crrev.com/09de997b3504368d40644afa7310b90faff5d09c
Cr-Commit-Position: refs/heads/master@{#30442}

[Benedikt Meurer, 2015-08-28 12:15:23]

Hey Yang,

Next step to make builtins object obsolete. More to
come in followup CLs.
Please take a look.

Thanks,
Benedikt

[Yang, 2015-08-28 12:21:25]

On 2015/08/28 12:15:23, Benedikt Meurer wrote:
> Hey Yang,
> 
> Next step to make builtins object obsolete. More to
> come in followup CLs.
> Please take a look.
> 
> Thanks,
> Benedikt

lgtm.

[Michael Starzinger, 2015-08-28 12:24:43]

LGTM on TurboFan, didn't look at the rest.

[Benedikt Meurer, 2015-08-28 12:24:53]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2015-08-28 12:25:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1319973007/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1319973007/1

[commit-bot: I haz the power, 2015-08-28 12:59:56]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-28 13:00:19]

Patchset 1 (id:??) landed as
https://crrev.com/09de997b3504368d40644afa7310b90faff5d09c
Cr-Commit-Position: refs/heads/master@{#30442}