Support compilation of Hello World

tests/compiler/dart2js/deferred_follow_constant_dependencies_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.
 
 // Test that constants depended on by other constants are correctly deferred.
 
 import 'package:async_helper/async_helper.dart';
+import 'package:compiler/src/common.dart';
 import 'package:compiler/src/constants/values.dart';
 import 'package:compiler/src/compiler.dart';
 import 'package:expect/expect.dart';
 import 'memory_compiler.dart';
 
 void main() {
   asyncTest(() async {
     CompilationResult result =
         await runCompiler(memorySourceFiles: MEMORY_SOURCE_FILES);
     Compiler compiler = result.compiler;
     var outputUnitForElement = compiler.deferredLoadTask.outputUnitForElement;
     var outputUnitForConstant = compiler.deferredLoadTask.outputUnitForConstant;
     var mainOutputUnit = compiler.deferredLoadTask.mainOutputUnit;
     var lib =
         compiler.libraryLoader.lookupLibrary(Uri.parse("memory:lib.dart"));
     var backend = compiler.backend;
     List<ConstantValue> allConstants = [];
 
     addConstantWithDependendencies(ConstantValue c) {
       allConstants.add(c);
       c.getDependencies().forEach(addConstantWithDependendencies);
     }
 
     backend.constants.compiledConstants.forEach(addConstantWithDependendencies);
     for (String stringValue in ["cA", "cB", "cC"]) {
       ConstantValue constant = allConstants.firstWhere((constant) {
         return constant.isString
             && constant.primitiveValue.slowToString() == stringValue;
       });
-      Expect.notEquals(null, outputUnitForConstant(constant));
-      Expect.notEquals(mainOutputUnit, outputUnitForConstant(constant));
+      Expect.notEquals(null, outputUnitForConstant(constant),
+          "Constant value ${constant.toStructuredText()} has no output unit.");
+      Expect.notEquals(mainOutputUnit, outputUnitForConstant(constant),
+          "Constant value ${constant.toStructuredText()} "
+              "is in the main output unit.");
     }
   });
 }
 
 // The main library imports lib1 and lib2 deferred and use lib1.foo1 and
 // lib2.foo2.  This should trigger seperate outputunits for main, lib1 and lib2.
 //
 // Both lib1 and lib2 import lib3 directly and
 // both use lib3.foo3.  Therefore a shared output unit for lib1 and lib2 should
 // be created.
 //
 // lib1 and lib2 also import lib4 deferred, but lib1 uses lib4.bar1 and lib2
 // uses lib4.bar2.  So two output units should be created for lib4, one for each
 // import.
 const Map MEMORY_SOURCE_FILES = const {"main.dart": """
 import 'lib.dart' deferred as lib;
 
 void main() {
   print(lib.L);
 }
 """, "lib.dart": """
 class C {
   final a;
   const C(this.a);
 }
 
 const L = const {"cA": const C(const {"cB": "cC"})};
 """,};