Move FindCodeObject from Heap to Isolate.

Move FindCodeObject from Heap to Isolate.

This removes the isolate=>heap=>isolate nonsense and has the additional bonus
that it re-enables printing of code objects in GDB. NOT: To make the latter
work, one has to adapt GDB any macros using FindCodeObject! Keeping things as it
is and outlining Isolate::heap() was not really an option...

Side note: Currently we are lucky that we still have Isolate::Current()
available in GDB, although it is marked as INLINE. :-}

R=verwaest@chromium.org

Committed: http://code.google.com/p/v8/source/detail?r=15770

[Toon Verwaest, 2013-07-19 09:38:35]

lgtm++

[Sven Panne, 2013-07-19 09:39:10]

Committed patchset #1 manually as r15770 (presubmit successful).