Fix memory leaks in ~Zone and ~Isolate

Fix memory leaks in ~Zone and ~Isolate

TEST=chromium valgrind bots

Committed: http://code.google.com/p/v8/source/detail?r=8949

[Jakob Kummerow, 2011-08-16 17:01:46]

PTAL.

The actual change is minimal: I simply put a "delete" operator, guarded by a
NULL check, into the d'tors of Zone and Isolate. To make it work, I additionally
had to move the class definitions of Segment and ExternalReferenceTable around
to make their d'tors visible to where the "delete" operator is used.

[Vitaly Repeshko, 2011-08-16 17:52:30]

LGTM with comments addressed.

http://codereview.chromium.org/7660016/diff/1/src/isolate.cc
File src/isolate.cc (right):

http://codereview.chromium.org/7660016/diff/1/src/isolate.cc#newcode1594
src/isolate.cc:1594: if (external_reference_table_ != NULL) {
It's safe to delete NULL. "if" is not necessary.

http://codereview.chromium.org/7660016/diff/1/src/zone.cc
File src/zone.cc (right):

http://codereview.chromium.org/7660016/diff/1/src/zone.cc#newcode82
src/zone.cc:82: delete segment_head_;
This should use DeleteSegment.

http://codereview.chromium.org/7660016/diff/1/src/zone.h
File src/zone.h (right):

http://codereview.chromium.org/7660016/diff/1/src/zone.h#newcode61
src/zone.h:61: ~Zone();
Given that the constructor is private it makes sense to have the destructor
private too (if possible).

[Jakob Kummerow, 2011-08-17 08:47:29]

Comments addressed, landing.

http://codereview.chromium.org/7660016/diff/1/src/isolate.cc
File src/isolate.cc (right):

http://codereview.chromium.org/7660016/diff/1/src/isolate.cc#newcode1594
src/isolate.cc:1594: if (external_reference_table_ != NULL) {
On 2011/08/16 17:52:32, Vitaly Repeshko wrote:
> It's safe to delete NULL. "if" is not necessary.

Done.

http://codereview.chromium.org/7660016/diff/1/src/zone.cc
File src/zone.cc (right):

http://codereview.chromium.org/7660016/diff/1/src/zone.cc#newcode82
src/zone.cc:82: delete segment_head_;
On 2011/08/16 17:52:32, Vitaly Repeshko wrote:
> This should use DeleteSegment.

Done.
This required putting the code into a separate method, because DeleteSegment()
depends on the isolate's counters being alive, but at the time ~Zone() runs
they're already deleted.

http://codereview.chromium.org/7660016/diff/1/src/zone.h
File src/zone.h (right):

http://codereview.chromium.org/7660016/diff/1/src/zone.h#newcode61
src/zone.h:61: ~Zone();
On 2011/08/16 17:52:32, Vitaly Repeshko wrote:
> Given that the constructor is private it makes sense to have the destructor
> private too (if possible).

Done.