Migrate language/arithmetic2_test ... language/async_await_syntax_test.

tests/language_2/assertion_initializer_const_function_test.dart

 // Copyright (c) 2017, 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 {
   static bool staticTrue() => true;
   final int x;
   const C(this.x);
   // The expression *is* compile-time constant, but not a bool value.
   // Static warning, runtime always fails assertion.
   const C.bc01(this.x, y)
       : assert(staticTrue)  //# 01: static type warning
       ;
 }
 
 main() {
   bool checkedMode = false;
   assert(checkedMode = true);
   if (checkedMode) {                                              //# 01: continued
     Expect.throws(() => new C.bc01(1, 2), (e) => e is TypeError); //# 01: continued
   } else {                                                        //# 01: continued
     Expect.equals(1, new C.bc01(1, 2).x);
   }                                                               //# 01: continued
 }