Do not share type arguments of mixin types, but clone them to avoid finalization

Do not share type arguments of mixin types, but clone them to avoid finalization
errors when cycles are involved (issue 13688).
Add regression test.

R=hausner@google.com

Committed: https://code.google.com/p/dart/source/detail?r=28107

[regis, 2013-10-01 17:40:00]

Adding Matthias as reviewer, since Ivan may be busy.

[hausner, 2013-10-01 18:20:51]

LGTM.

[regis, 2013-10-01 18:26:29]

Committed patchset #1 manually as r28107 (presubmit successful).

[Ivan Posva, 2013-10-01 18:50:03]

Please explain why we are not using the reusable handles. We cannot see the
recursion through NumTypeArguments anywhere.

Thanks,
-Ivan

https://codereview.chromium.org/25569002/diff/1/runtime/vm/object.cc
File runtime/vm/object.cc (right):

https://codereview.chromium.org/25569002/diff/1/runtime/vm/object.cc#newcode1712
runtime/vm/object.cc:1712: Class& cls = Class::Handle(isolate);
Why was this changed?

[regis, 2013-10-01 19:11:57]

The number of type arguments depends on the number of type parameters, which, in
case of a mixin application class, depends on the type parameters of the mixin
types.

In other words, NumTypeArguments() calls NumTypeParameters(), which calls
ApplyMixinType(), which will finalize the mixin types. Add some fun declarations
to the mix, and NumTypeArguments() ends up being called recursively.

https://codereview.chromium.org/25569002/diff/1/runtime/vm/object.cc
File runtime/vm/object.cc (right):

https://codereview.chromium.org/25569002/diff/1/runtime/vm/object.cc#newcode1712
runtime/vm/object.cc:1712: Class& cls = Class::Handle(isolate);
On 2013/10/01 18:50:04, Ivan Posva wrote:
> Why was this changed?

We were just lucky before. NumTypeArguments() is reentrant.