Heap profiler: fix removed DOM wrappers reporting.

Heap profiler: fix removed DOM wrappers reporting.

Aggregated snapshots: don't report unreachable objects.
Full snapshots: restore forcing GC prior to taking a snapshot.

I played with the repro page provided for the bug and found that GC
must be performed prior to taking a snapshot even if we only report
reachable objects. GC allows weak handles to finalize.  Now heap
profiler produces aligned results for the repro page in both modes.

BUG=crbug/70434
TEST=none

Committed: http://code.google.com/p/v8/source/detail?r=6598

[Søren Thygesen Gjesse, 2011-02-03 08:43:26]

LGTM

For DOM wrappers sometimes more GCs can free more, but we probably do not want
to do more than one GC before taking the snapshot.