Fix analyzer's treatment of mixin constructors.

tests/language/mixin_super_constructor_positionals_test.dart

Index: tests/language/mixin_super_constructor_positionals_test.dart
diff --git a/tests/language/mixin_super_constructor_positionals_test.dart b/tests/language/mixin_super_constructor_positionals_test.dart
index 215ae205ffed090531deab359ca4addd77104ad1..289822d4535119a07e48340c237e351c73c14dd3 100644
--- a/tests/language/mixin_super_constructor_positionals_test.dart
+++ b/tests/language/mixin_super_constructor_positionals_test.dart
@@ -6,7 +6,11 @@ import "package:expect/expect.dart";
 
 class Base {
   int i, j;
-  Base.ctor(int this.i, [int this.j = 10]);
+  Base.ctor(int this.i,
+            [                  /// 01: compile-time error
+            int this.j
+            ]                  /// 01: continued
+           );
 }
 
 abstract class M {
@@ -19,7 +23,7 @@ abstract class M {
 class C extends Base with M {
   int l = 131;
   C.foo() : super.ctor(1, 13);
-  C.bar() : super.ctor(1);
+  C.bar() : super.ctor(1);     /// 01: continued
 }
 
 main() {
@@ -29,10 +33,5 @@ main() {
   Expect.equals(14, c1.foo());
   Expect.equals(42, c1.k);
   Expect.equals(131, c1.l);
-  C c2 = new C.bar();
-  Expect.equals(1, c2.i);
-  Expect.equals(10, c2.j);
-  Expect.equals(11, c2.foo());
-  Expect.equals(42, c2.k);
-  Expect.equals(131, c2.l);
+  C c2 = new C.bar();          /// 01: continued
 }