Fixes for super tearoff in constructor

tests/language_strong/super_tearoff_test.dart

+import 'package:expect/expect.dart';

[Jennifer Messerly, 2017/06/19 20:24:52]

this needs a copyright notice

alternatively, I think you could easily add this to an existing test. I always
try and consolidate very simple tests, because compiling+running individual
language tests adds lots of buildbot and iteration cycle slowness.

super_from_constructor_test.dart seems like a good place :)

[vsm, 2017/06/19 20:36:20]

Done.

+
+int invoke(int f()) => f();
+
+class A {
+  int foo() {
+    return 42;
+  }
+}
+
+class B extends A {
+  int x;
+
+  B() {
+    x = invoke(super.foo);
+  }
+
+  int foo() {
+    return -1;
+  }
+}
+
+void main() {
+  var b = new B();
+  Expect.equals(42, b.x);
+}