Add fatal-warnings flag, that turns warnings into compilation errors (the name

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 64 matching lines @@
             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'),
             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'),
             allowNativeExtensions:
                 hasOption(options, '--allow-native-extensions')) {
     tasks.addAll([
         userHandlerTask = new leg.GenericTask('Diagnostic handler', this),
         userProviderTask = new leg.GenericTask('Input provider', this),
     ]);
@@ skipping 252 matching lines @@
           ' unaccounted ${total - cumulated}msec');
       return success;
     });
   }
 
   void reportDiagnostic(leg.Spannable node,
                         leg.Message message,
                         api.Diagnostic kind) {
     leg.SourceSpan span = spanFromSpannable(node);
     if (identical(kind, api.Diagnostic.ERROR)
-        || identical(kind, api.Diagnostic.CRASH)) {
+        || identical(kind, api.Diagnostic.CRASH)
+        || (fatalWarnings && identical(kind, api.Diagnostic.WARNING))) {
       compilationFailed = true;
     }
     // [:span.uri:] might be [:null:] in case of a [Script] with no [uri]. For
     // instance in the [Types] constructor in typechecker.dart.
     if (span == null || span.uri == null) {
       callUserHandler(null, null, null, '$message', kind);
     } else {
       callUserHandler(
           translateUri(null, span.uri), span.begin, span.end, '$message', kind);
     }
@@ skipping 31 matching lines @@
     print('$message: ${tryToString(exception)}');
     print(tryToString(stackTrace));
   }
 
   fromEnvironment(String name) => environment[name];
 
   LibraryInfo lookupLibraryInfo(String libraryName) {
     return library_info.LIBRARIES[libraryName];
   }
 }