VM: Make ZoneAllocated-objects that don't need a vtable smaller.

VM: Make ZoneAllocated-objects that don't need a vtable smaller.

Remove virtual destructor from ZoneAllocated. Instead, subclasses
that need one have it explicitly declared.

This makes ZoneAllocated objects without virtual functions smaller
because there won't be a vtable for them.

R=srdjan@google.com

Committed: https://code.google.com/p/dart/source/detail?r=37228

[srdjan, 2014-06-06 15:02:56]

How do you now catch that someone does not mistakenly call delete on a
ZoneAllocated object? May add default destructor with UNREACHABLE in debug mdoe
only?

[Florian Schneider, 2014-06-10 08:44:04]

On 2014/06/06 15:02:56, srdjan wrote:
> How do you now catch that someone does not mistakenly call delete on a
> ZoneAllocated object? May add default destructor with UNREACHABLE in debug
mdoe
> only?

I don't understand: I did not change the delete operator and the delete operator
of ZoneAllocated already has UNREACHABLE().

[srdjan, 2014-06-10 14:25:36]

lgtm

[Florian Schneider, 2014-06-11 10:54:26]

Committed patchset #1 manually as r37228 (presubmit successful).