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

pkg/compiler/lib/src/dart2js.dart

 // Copyright (c) 2013, 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 dart2js.cmdline;
 
 import 'dart:async'
     show Future, EventSink;
 import 'dart:convert' show UTF8, LineSplitter;
 import 'dart:io'
@@ skipping 278 matching lines @@
   }
 
   List<String> arguments = <String>[];
   List<OptionHandler> handlers = <OptionHandler>[
     new OptionHandler('-[chvm?]+', handleShortOptions),
     new OptionHandler('--throw-on-error(?:=[0-9]+)?', handleThrowOnError),
     new OptionHandler('--suppress-warnings', (_) {
       diagnosticHandler.showWarnings = false;
       passThrough('--suppress-warnings');
     }),
+    new OptionHandler('--fatal-warnings', passThrough),
     new OptionHandler('--suppress-hints',
                       (_) => diagnosticHandler.showHints = false),
     new OptionHandler(
         '--output-type=dart|--output-type=dart-multi|--output-type=js',
         setOutputType),
     new OptionHandler('--verbose', setVerbose),
     new OptionHandler('--version', (_) => wantVersion = true),
     new OptionHandler('--library-root=.+', setLibraryRoot),
     new OptionHandler('--out=.+|-o.*', setOutput, multipleArguments: true),
     new OptionHandler('--allow-mock-compilation', passThrough),
@@ skipping 246 matching lines @@
   --analyze-only
     Analyze but do not generate code.
 
   --analyze-signatures-only
     Skip analysis of method bodies and field initializers. This option implies
     --analyze-only.
 
   --suppress-warnings
     Do not display any warnings.
 
+  --fatal-warnings
+    Treat warnings as compilation errors.
+
   --suppress-hints
     Do not display any hints.
 
   --enable-diagnostic-colors
     Add colors to diagnostic messages.
 
   --terse
     Emit diagnostics without suggestions for how to get rid of the diagnosed
     problems.
 
@@ skipping 158 matching lines @@
       } else if (exitCode == 253) {
         print(">>> TEST CRASH");
       } else {
         print(">>> TEST FAIL");
       }
       stderr.writeln(">>> EOF STDERR");
       subscription.resume();
     });
   });
 }