Support parameter metadata.

tests/compiler/dart2js/unparser_test.dart

 // Copyright (c) 2012, 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.
 
 import "package:expect/expect.dart";
 import 'parser_helper.dart';
 import 'mock_compiler.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/tree/tree.dart';
 
 testUnparse(String statement) {
@@ skipping 319 matching lines @@
   testUnparseParameters(
       ["this.foo", "this.bar=0", "int this.baz", "int this.boz=0"]);
   testUnparseParameters(
       ["foo()", "void bar()", "int baz(a)", "int boz(int a,int b)=null"]);
   testUnparseParameters(
       ["this.foo()",
        //"void this.bar()", // Commented out due to Issue 7852
        //"int this.baz(a)", // Commented out due to Issue 7852
        //"int this.boz(int a,int b)=null" // Commented out due to Issue 7852
        ]);
+  testUnparseParameters(
+      ["@a foo", "@b @c bar=0", "@D(0) int baz", "@E([f],{g:h}) int boz=0"]);
 }
 
 testSymbolLiterals() {
   testUnparse("#+;");
   testUnparse("#-;");
   testUnparse("#*;");
   testUnparse("#/;");
   testUnparse("#~/;");
   testUnparse("#%;");
   testUnparse("#<;");
@@ skipping 27 matching lines @@
   testExport();
   testPart();
   testPartOf();
   testCombinators();
   testRedirectingFactoryConstructors();
   testClassDeclarations();
   testMixinApplications();
   testParameters();
   testSymbolLiterals();
 }