Add --analyze-signatures-only option to dart2js

sdk/lib/_internal/compiler/implementation/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:uri';
 import 'dart:async';
 
 import '../compiler.dart' as api;
@@ skipping 26 matching lines @@
             outputProvider: outputProvider,
             enableTypeAssertions: hasOption(options, '--enable-checked-mode'),
             enableUserAssertions: hasOption(options, '--enable-checked-mode'),
             enableMinification: hasOption(options, '--minify'),
             enableNativeLiveTypeAnalysis:
                 !hasOption(options, '--disable-native-live-type-analysis'),
             emitJavaScript: !hasOption(options, '--output-type=dart'),
             disallowUnsafeEval: hasOption(options, '--disallow-unsafe-eval'),
             analyzeAll: hasOption(options, '--analyze-all'),
             analyzeOnly: hasOption(options, '--analyze-only'),
+            analyzeSignaturesOnly:
+                hasOption(options, '--analyze-signatures-only'),
             rejectDeprecatedFeatures:
                 hasOption(options, '--reject-deprecated-language-features'),
             checkDeprecationInSdk:
                 hasOption(options,
                           '--report-sdk-use-of-deprecated-language-features'),
             strips: getStrips(options),
             enableConcreteTypeInference:
                 hasOption(options, '--enable-concrete-type-inference'),
             preserveComments: hasOption(options, '--preserve-comments')) {
     if (!libraryRoot.path.endsWith("/")) {
@@ skipping 200 matching lines @@
       handler(translateUri(span.uri, null), span.begin, span.end,
               message, kind);
     }
   }
 
   bool get isMockCompilation {
     return mockableLibraryUsed
       && (options.indexOf('--allow-mock-compilation') != -1);
   }
 }