Add option for outputting a deferred loading mapping.

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 '../compiler.dart' as api;
 import 'dart2jslib.dart' as leg;
@@ skipping 52 matching lines @@
             strips: extractCsvOption(options, '--force-strip='),
             enableConcreteTypeInference:
                 hasOption(options, '--enable-concrete-type-inference'),
             disableTypeInferenceFlag:
                 hasOption(options, '--disable-type-inference'),
             preserveComments: hasOption(options, '--preserve-comments'),
             verbose: hasOption(options, '--verbose'),
             sourceMapUri: extractUriOption(options, '--source-map='),
             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'),
             hasIncrementalSupport:
                 forceIncrementalSupport ||
                 hasOption(options, '--incremental-support'),
@@ skipping 301 matching lines @@
     print('$message: ${tryToString(exception)}');
     print(tryToString(stackTrace));
   }
 
   fromEnvironment(String name) => environment[name];
 
   LibraryInfo lookupLibraryInfo(String libraryName) {
     return library_info.LIBRARIES[libraryName];
   }
 }