Handle const Symbol(...) in kernel_impact

tests/compiler/dart2js/kernel/impact_test.dart

 // Copyright (c) 2016, 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.
 
 library dart2js.kernel.impact_test;
 
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/commandline_options.dart';
 import 'package:compiler/src/common.dart';
 import 'package:compiler/src/common/names.dart';
@@ skipping 37 matching lines @@
   testNull();
   testTrue();
   testFalse();
   testInt();
   testDouble();
   testString();
   testStringInterpolation();
   testStringInterpolationConst();
   testStringJuxtaposition();
   testSymbol();
+  testConstSymbol();
   testTypeLiteral();
   testBoolFromEnvironment();
   testEmptyListLiteral();
   testEmptyListLiteralDynamic();
   testEmptyListLiteralTyped();
   testEmptyListLiteralConstant();
   testNonEmptyListLiteral();
   testEmptyMapLiteral();
   testEmptyMapLiteralDynamic();
   testEmptyMapLiteralTyped();
@@ skipping 140 matching lines @@
 testFalse() => false;
 testInt() => 42;
 testDouble() => 37.5;
 testString() => 'foo';
 testStringInterpolation() => '${0}';
 testStringInterpolationConst() {
   const b = '${0}';
 }
 testStringJuxtaposition() => 'a' 'b';
 testSymbol() => #main;
+testConstSymbol() => const Symbol('main');
 testTypeLiteral() => Object;
 testBoolFromEnvironment() => const bool.fromEnvironment('FOO');
 testEmptyListLiteral() => [];
 testEmptyListLiteralDynamic() => <dynamic>[];
 testEmptyListLiteralTyped() => <String>[];
 testEmptyListLiteralConstant() => const [];
 testNonEmptyListLiteral() => [0];
 testEmptyMapLiteral() => {};
 testEmptyMapLiteralDynamic() => <dynamic, dynamic>{};
 testEmptyMapLiteralTyped() => <String, int>{};
@@ skipping 691 matching lines @@
         visitList(type.optionalParameterTypes),
         type.namedParameters,
         visitList(type.namedParameterTypes));
   }
 }
 
 /// Perform unaliasing of all typedefs nested within a [ResolutionDartType].
 ResolutionDartType unalias(ResolutionDartType type) {
   return const Unaliaser().visit(type);
 }