Fix ReturnValue::Set.

Make ReturnValue a friend of Persistent, so it can use operator*.

BUG=
R=dcarney@chromium.org, svenpanne@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=14999

[marja, 2013-06-06 15:07:39]

dcarney@, ptal. I was under the impression that v8 is already
post-handlepocalyptic, but doesn't seem so. Maybe this was missed because the
code is inside a template which was not instantiated by tests?

[dcarney, 2013-06-06 18:09:59]

On 2013/06/06 15:07:39, marja wrote:
> dcarney@, ptal. I was under the impression that v8 is already
> post-handlepocalyptic, but doesn't seem so. Maybe this was missed because the
> code is inside a template which was not instantiated by tests?

just use the handle value directly - returnvalue should be a friend class of
persistent

[marja, 2013-06-07 09:58:41]

alright, made it a friend instead

[dcarney, 2013-06-07 10:39:45]

lgtm

[marja, 2013-06-07 10:41:22]

svenpanne@, ptal

[Sven Panne, 2013-06-07 10:42:54]

lgtm

[dcarney, 2013-06-07 10:46:57]

Committed patchset #2 manually as r14999 (presubmit successful).