Fix bad optimization prematurely marking types as instantiated (issue 8710).

tests/language/generics3_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.
+//
+// Dart test program testing generic type allocations and generic type tests.
+// Regression test for issue 8710.
+
+class C1<T> {}
+class C2<T> {}
+class C3<T> extends C2<C1<T>> {}
+class C4<T> extends C3<T> { f() => new C5<C1<T>>(new C1<T>()); }
+class C5<T> { C5(T x); }  // Checked mode: x must be of type C1<String>.
+
+main() {
+  new C4<String>().f();
+}