Add JS globals to guest-created iframes.

For guests with DOM access, the copyToImports is done in a function
passed to Domado rather than separately in the frame group. This
refactoring allows virtual documents for iframes to also obtain their
imports.

Note that host-provided extra imports will _not_ be added to iframes;
There is no especially strong reason for this behavior, but it was
simpler and fits with (in browsers in general) iframes being a way to
create a "fresh" environment with no application-specific global state.

@r5593

[kpreid_google, 2013-09-09 17:56:06]

ping

[felix8a, 2013-09-09 18:05:42]

lgtm

> Note that host-provided extra imports will _not_ be added to iframes;
> there is no strong reason for this, however.

maybe add a note somewhere about that?

[kpreid_google, 2013-09-09 18:46:43]

On 2013/09/09 18:05:42, felix8a wrote:
> > Note that host-provided extra imports will _not_ be added to iframes;
> > there is no strong reason for this, however.
> 
> maybe add a note somewhere about that?

Done.