Migrate language block 46 - canonical_const ... char_escape.

tests/language_2/cha_deopt3_test.dart

 // Copyright (c) 2014, 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=--optimization-counter-threshold=100
+// VMOptions=--optimization-counter-threshold=100 --no-background-compilation
+// VMOptions=--optimization-counter-threshold=100 --no-background-compilation --no-use-field-guards
 
 // Test lazy deoptimization at type checks with interface implementation.
 
 import "package:expect/expect.dart";
 import "cha_deopt3_lib.dart";
 import "cha_deopt3_deferred_lib.dart" deferred as d;
 
 var loaded = false;
 
 main() {
@@ skipping 15 matching lines @@
   } catch (e) {}
 }
 
 bla() {
   var count = 0;
   for (var x in make_array()) {
     if (x is T) count++;
   }
   return count;
 }