Handle constant ?? expressions in constructors.

pkg/compiler/lib/src/dart2js.dart

 // Copyright (c) 2013, 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.cmdline;
 
 import 'dart:async' show EventSink, Future;
 import 'dart:convert' show UTF8, LineSplitter;
 import 'dart:io' show exit, File, FileMode, Platform, stdin, stderr;
 
@@ skipping 518 matching lines @@
   }
 
   Uri script = currentDirectory.resolve(arguments[0]);
   CompilerOptions compilerOptions = new CompilerOptions.parse(
       entryPoint: script,
       libraryRoot: libraryRoot,
       packageRoot: packageRoot,
       packageConfig: packageConfig,
       packagesDiscoveryProvider: findPackages,
       resolutionInputs: resolutionInputs,
-      resolutionOutput: resolveOnly ? resolutionOutput: null,
+      resolutionOutput: resolveOnly ? resolutionOutput : null,
       options: options,
       environment: environment);
   return compileFunc(
           compilerOptions, inputProvider, diagnosticHandler, outputProvider)
       .then(compilationDone);
 }
 
 class AbortLeg {
   final message;
   AbortLeg(this.message);
@@ skipping 471 matching lines @@
   @override
   void close() {
     // Do nothing.
   }
 
   @override
   void addError(errorEvent, [StackTrace stackTrace]) {
     // Ignore
   }
 }