dart2js: Add --fast-startup flag.

pkg/compiler/lib/src/apiimpl.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.
 
 library leg_apiimpl;
 
 import 'dart:async';
 import 'dart:convert';
 
 import '../compiler_new.dart' as api;
@@ skipping 75 matching lines @@
             outputUri: extractUriOption(options, '--out='),
             terseDiagnostics: hasOption(options, '--terse'),
             deferredMapUri: extractUriOption(options, '--deferred-map='),
             dumpInfo: hasOption(options, '--dump-info'),
             buildId: extractStringOption(
                 options, '--build-id=',
                 "build number could not be determined"),
             showPackageWarnings:
                 hasOption(options, '--show-package-warnings'),
             useContentSecurityPolicy: hasOption(options, '--csp'),
+            useStartupEmitter: hasOption(options, '--fast-startup'),
             hasIncrementalSupport:
                 forceIncrementalSupport ||
                 hasOption(options, '--incremental-support'),
             suppressWarnings: hasOption(options, '--suppress-warnings'),
             fatalWarnings: hasOption(options, '--fatal-warnings'),
             enableExperimentalMirrors:
                 hasOption(options, '--enable-experimental-mirrors'),
             generateCodeWithCompileTimeErrors:
                 hasOption(options, '--generate-code-with-compile-time-errors'),
             testMode: hasOption(options, '--test-mode'),
@@ skipping 371 matching lines @@
     print('$message: ${tryToString(exception)}');
     print(tryToString(stackTrace));
   }
 
   fromEnvironment(String name) => environment[name];
 
   LibraryInfo lookupLibraryInfo(String libraryName) {
     return library_info.LIBRARIES[libraryName];
   }
 }