Make the GC aware of JSReceiver pointers in LookupResults.

Make the GC aware of JSReceiver pointers in LookupResults.

The LookupResult utility class is used in handlified code, but it can
contain a raw pointer to the lookup's holder object.  Create a per-thread
stack of live LookupResults and iterate all the live ones on GC.

R=vegorov@chromium.org,erik.corry@gmail.com
BUG=
TEST=

Committed: http://code.google.com/p/v8/source/detail?r=9676

[Kevin Millikin (Chromium), 2011-10-18 09:07:32]

Context for this change: we already have a potentially unsafe of this class, and
we'd like to use it more but it's not safe.

Morally, this makes it a handle.  Should I expose a function something like
this?:

Handle<JSObject> holder_handle() {
  ASSERT(holder_->IsJSObject());
  return Handle<JSObject>(reinterpret_cast<JSObject**>(&holder_));
}

[Vyacheslav Egorov (Chromium), 2011-10-18 10:59:38]

lgtm