Implement override checks.

dart/lib/compiler/implementation/dart2js.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('dart2js');
 
 #import('dart:io');
 #import('dart:uri');
 #import('dart:utf');
 
@@ skipping 176 matching lines @@
       // TODO(podivilov): We should find a better way to return source maps from
       // emitter. Using diagnostic handler for that purpose is a temporary hack.
       writeString(sourceMapOut, message);
       return;
     }
 
     if (isAborting) return;
     isAborting = kind === api.Diagnostic.CRASH;
     bool fatal = (kind.ordinal & FATAL) != 0;
     bool isInfo = (kind.ordinal & INFO) != 0;
-    if (isInfo) {
-      assert(uri === null);
+    if (isInfo && uri === null && kind !== api.Diagnostic.INFO) {
       info(message, kind);
       return;
     }
     var color;
     if (!enableColors) {
       color = (x) => x;
     } else if (kind === api.Diagnostic.ERROR) {
       color = colors.red;
     } else if (kind === api.Diagnostic.WARNING) {
       color = colors.magenta;
     } else if (kind === api.Diagnostic.LINT) {
       color = colors.magenta;
     } else if (kind === api.Diagnostic.CRASH) {
       color = colors.red;
+    } else if (kind === api.Diagnostic.INFO) {
+      color = colors.green;
     } else {
       throw 'Unknown kind: $kind (${kind.ordinal})';
     }
     if (uri === null) {
       assert(fatal);
       print(color(message));
     } else if (fatal || showWarnings) {
       SourceFile file = sourceFiles[uri.toString()];
       print(file.getLocationMessage(color(message), begin, end, true,
                                     color));
@@ skipping 151 matching lines @@
     } catch (var ignored) {
       print('Internal error: error while printing exception');
     }
     try {
       print(trace);
     } finally {
       exit(253); // 253 is recognized as a crash by our test scripts.
     }
   }
 }