Change --hide-package-warnings to --show-package-warnings and add hint on suppress warnings.

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:async';
 
 import '../compiler.dart' as api;
 import 'dart2jslib.dart' as leg;
@@ skipping 45 matching lines @@
             disableTypeInferenceFlag:
                 hasOption(options, '--disable-type-inference'),
             preserveComments: hasOption(options, '--preserve-comments'),
             verbose: hasOption(options, '--verbose'),
             sourceMapUri: extractSourceMapUri(options),
             terseDiagnostics: hasOption(options, '--terse'),
             dumpInfo: hasOption(options, '--dump-info'),
             buildId: extractStringOption(
                 options, '--build-id=',
                 "build number could not be determined"),
-            hidePackageWarnings:
-                hasOption(options, '--hide-package-warnings')) {
+            showPackageWarnings:
+                hasOption(options, '--show-package-warnings')) {
     if (!libraryRoot.path.endsWith("/")) {
       throw new ArgumentError("libraryRoot must end with a /");
     }
     if (packageRoot != null && !packageRoot.path.endsWith("/")) {
       throw new ArgumentError("packageRoot must end with a /");
     }
   }
 
   static String extractStringOption(List<String> options,
                                     String prefix,
@@ skipping 253 matching lines @@
   }
 
   void diagnoseCrashInUserCode(String message, exception, stackTrace) {
     hasCrashed = true;
     print('$message: ${tryToString(exception)}');
     print(tryToString(stackTrace));
   }
 
   fromEnvironment(String name) => environment[name];
 }