new persistent semantics

new persistent semantics

R=marja, jochen, svenpanne@chromium.org, mstarzinger@chromium.org,
BUG=

[dcarney, 2013-06-20 14:19:52]

so here's what I had in mind, there's lots of work to do, and there's a few
functions left unimplemented.  this patch should apply and build all of chrome
just fine, but there are lots of places where additionally parameters will be
needed for Persistent.  anyway, the order of things would then be

1. create a template parameter for Persistent that does correct copying and
autodisposes
2. convert chrome to use it everywhere
3. make the new parameter the default
4 get rid of functions like Dispose, Clear, ClearAndLeak, AutoDispose

[dcarney, 2013-06-26 08:52:53]

I had some additional thoughts on this:

it might be better to have GlobalHandles::Node keep the pointer to the
persistent, so on move and copy it's easy to relocate automatically, then
WeakDispose could just return a bool instead and we could optimize for the case
of always returning true or always returning false.  Also, the weak callback
could always return the pointer to the original persistent, which would be
ideal, since the caller could just Reset it properly from there.  I would still
pass the Handle on the stack as well since it should be cheap and allows us not
to deal with new handles in callbacks in the common case.

[dcarney, 2013-06-26 08:54:39]

adding sven and michael to the party.

Note: this is a major work in progress, and needs lots of input.

[dcarney, 2013-08-06 17:05:42]

closing issue for now since no one had time to pick it up while i was away
will create a new one when ready