Add assert-in-initializer-list to formal specification.

tests/language/assertion_initializer_const_error2_test.dart

+// Copyright (c) 201, 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.
+// VMOptions=--assert_initializer
+//
+// Dart test program testing assert statements.
+
+import "package:expect/expect.dart";
+
+class C {
+  final int x;
+  // Const constructors.
+  const C.cc01(this.x, y) : assert(x < y);
+  const C.cc02(x, y) : x = x, assert(x < y);
+  const C.cc03(x, y) : assert(x < y), x = x;
+  const C.cc04(this.x, y) : super(), assert(x < y);
+  const C.cc05(this.x, y) : assert(x < y), super();
+  const C.cc06(x, y) : x = x, super(), assert(x < y);
+  const C.cc07(x, y) : assert(x < y), super(), x = x;
+  const C.cc08(x, y) : assert(x < y), super(), x = x, assert(y > x);
+  const C.cc09(this.x, y) : assert(x < y, "$x < $y");
+  const C.cc10(this.x, y) : assert(x < y,);
+  const C.cc11(this.x, y) : assert(x < y, "$x < $y",);
+}
+
+
+main() {
+  // Failing assertions in const invociations are compile-time errors.
+  const C.cc01(2, 1);  //# cc01: compile-time error

[floitsch, 2017/06/29 12:08:56]

I would put the `//#` lines on the "assert" lines:

const C.cc01(this.x, y)
  : assert(x < y)  //# cc01: compile-time error
;

+  const C.cc02(2, 1);  //# cc02: compile-time error
+  const C.cc03(2, 1);  //# cc03: compile-time error
+  const C.cc04(2, 1);  //# cc04: compile-time error
+  const C.cc05(2, 1);  //# cc05: compile-time error
+  const C.cc06(2, 1);  //# cc06: compile-time error
+  const C.cc07(2, 1);  //# cc07: compile-time error
+  const C.cc08(2, 1);  //# cc08: compile-time error
+  const C.cc09(2, 1);  //# cc09: compile-time error
+  const C.cc10(2, 1);  //# cc10: compile-time error
+  const C.cc11(2, 1);  //# cc11: compile-time error
+}