Fix #29130: only consider classes allocated with generative constructors as potential closures

tests/compiler/dart2js_extra/29130_test.dart

+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// This is a regression test from issue #29310. The global type-inferrer does
+/// tracing of closures including allocated classes that implement a `call`
+/// method. We incorrectly considered also classes with invoked factory
+/// constructors, even if those were only abstract interfaces or mixins that
+/// weren't actually allocated explicitly.
+library regression_29130;
+
+main() {
+  new B();
+  new C();
+}
+
+class A {
+  call() {}
+}
+
+// interface scenario: we shouldn't trace B
+abstract class B implements A {
+  factory B() => null;
+}
+
+// mixin scenario: we should trace C, but we should trace _C
+abstract class C implements A {
+  factory C() => new D();
+}
+
+class D = A with C;