dart2js: retain constants that are used as annotations in constructors and setters.

tests/lib/mirrors/parameter_annotation_mirror_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.
 
 @MirrorsUsed(targets: "Foo")
 import "dart:mirrors";
 
 import 'package:expect/expect.dart';
 
 class ParameterAnnotation {
   final String value;
   const ParameterAnnotation(this.value);
 }
 
 class Foo {
+  Foo(@ParameterAnnotation("vogel") p) {}
+  Foo.named(@ParameterAnnotation("hamster") p) {}
+  Foo.named2(@ParameterAnnotation("hamster") p,
+             @ParameterAnnotation("wurm") p2) {}
+
   f1(@ParameterAnnotation("hest") p) {}
   f2(@ParameterAnnotation("hest") @ParameterAnnotation("fisk") p) {}
   f3(a, @ParameterAnnotation("fugl") p) {}
   f4(@ParameterAnnotation("fisk") a,
      {@ParameterAnnotation("hval") p}) {}
   f5(@ParameterAnnotation("fisk") a,
      [@ParameterAnnotation("hval") p]) {}
   f6({@ParameterAnnotation("fisk") z,
       @ParameterAnnotation("hval") p}) {}
+
+  set s1(@ParameterAnnotation("cheval") p) {}
 }
 
 expectAnnotations(Type type, Symbol method, int parameterIndex,
                   List<String> expectedValues) {
   MethodMirror mirror = reflectClass(type).declarations[method];
   ParameterMirror parameter = mirror.parameters[parameterIndex];
   List<InstanceMirror> annotations = parameter.metadata;
   Expect.equals(annotations.length, expectedValues.length,
                 "wrong number of parameter annotations");
   for (int i = 0; i < annotations.length; i++) {
     Expect.equals(expectedValues[i], annotations[i].reflectee.value,
                   "annotation #$i of parameter #$parameterIndex "
                   "of $type.$method.");
   }
 }
 
 main() {
+  expectAnnotations(Foo, #Foo, 0, ["vogel"]);
+  expectAnnotations(Foo, #Foo.named, 0, ["hamster"]);
+  expectAnnotations(Foo, #Foo.named2, 0, ["hamster"]);
+  expectAnnotations(Foo, #Foo.named2, 1, ["wurm"]);
+
   expectAnnotations(Foo, #f1, 0, ["hest"]);
   expectAnnotations(Foo, #f2, 0, ["hest", "fisk"]);
   expectAnnotations(Foo, #f3, 0, []);
   expectAnnotations(Foo, #f3, 1, ["fugl"]);
   expectAnnotations(Foo, #f4, 0, ["fisk"]);
   expectAnnotations(Foo, #f4, 1, ["hval"]);
   expectAnnotations(Foo, #f5, 0, ["fisk"]);
   expectAnnotations(Foo, #f5, 1, ["hval"]);
   expectAnnotations(Foo, #f6, 0, ["fisk"]);
   expectAnnotations(Foo, #f6, 1, ["hval"]);
+
+  expectAnnotations(Foo, const Symbol('s1='), 0, ["cheval"]);
 }