Enable DDC output to run on v8/d8 using ES6 modules

pkg/dev_compiler/lib/src/compiler/module_builder.dart

Index: pkg/dev_compiler/lib/src/compiler/module_builder.dart
diff --git a/pkg/dev_compiler/lib/src/compiler/module_builder.dart b/pkg/dev_compiler/lib/src/compiler/module_builder.dart
index 355f3effaf5c6f9e2c91b956a79e6606db96da2f..07510ebc9daf46b3523a3f185fed6461f0e76eae 100644
--- a/pkg/dev_compiler/lib/src/compiler/module_builder.dart
+++ b/pkg/dev_compiler/lib/src/compiler/module_builder.dart
@@ -212,7 +212,7 @@ class LegacyModuleBuilder extends _ModuleBuilder {
 /// Generates CommonJS modules (used by Node.js).
 class CommonJSModuleBuilder extends _ModuleBuilder {
   Program build(Program module) {
-    var importStatements = <Statement>[];
+    var importStatements = [js.statement("'use strict';"),];
 
     // Collect imports/exports/statements.
     visitProgram(module);
@@ -249,12 +249,7 @@ class CommonJSModuleBuilder extends _ModuleBuilder {
       }
     }
 
-    // TODO(vsm): See https://github.com/dart-lang/sdk/issues/27309
-    // This extra level of indirection should be unnecessary.
-    var block =
-        js.statement("(function() { 'use strict'; #; })()", [statements]);
-
-    return new Program([block]);
+    return new Program(statements);
   }
 }