Remove uses of String.operator+.

utils/template/world.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.
 
 /** The one true [World]. */
 World world;
 
 typedef void MessageHandler(String prefix, String message, SourceSpan span);
 typedef void PrintHandler(String message);
 
@@ skipping 54 matching lines @@
       // TODO(jimhug): Multiple spans cleaner...
       messageHandler(prefix, message, span);
       if (span1 != null) {
         messageHandler(prefix, message, span1);
       }
       if (span2 != null) {
         messageHandler(prefix, message, span2);
       }
     } else {
       final messageWithPrefix = options.useColors
-          ? (color + prefix + _NO_COLOR + message) : (prefix + message);
+          ? "$color$prefix$_NO_COLOR$message" : "$prefix$message";
 
       var text = messageWithPrefix;
       if (span != null) {
         text = span.toMessageString(messageWithPrefix);
       }
 
       String span1Text = span1 != null ?
           span1.toMessageString(messageWithPrefix) : "";
       String span2Text = span2 != null ?
           span2.toMessageString(messageWithPrefix) : "";
 
       if (printHandler == null) {
         print(text);
         if (span1 != null) {
           print(span1Text);
         }
         if (span2 != null) {
           print(span2Text);
         }
       } else {
         printHandler("${text}\r${span1Text}\r${span2Text}");
       }
     }
 
     if (throwing) {
-      throw new CompilerException(prefix + message, span);
+      throw new CompilerException("$prefix$message", span);
     }
   }
 
   /** [message] is considered a static compile-time error by the Dart lang. */
   void error(String message,
       [SourceSpan span, SourceSpan span1, SourceSpan span2]) {
     errors++;
     _message(_RED_COLOR, 'error: ', message,
         span, span1, span2, options.throwOnErrors);
   }
@@ skipping 48 matching lines @@
     sw.stop();
     info('$name in ${sw.elapsedInMs()}msec');
     return result;
   }
 }
 
 String _GREEN_COLOR = '\u001b[32m';
 String _RED_COLOR = '\u001b[31m';
 String _MAGENTA_COLOR = '\u001b[35m';
 String _NO_COLOR = '\u001b[0m';