Purge String operator+ from dart2js.

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 142 matching lines @@
 
   // TODO(ahe): We expect the future to be complete and call value
   // directly. In effect, we don't support truly asynchronous API.
   String code = api.compile(uri, libraryRoot, provider, handler, options).value;
   if (code === null) {
     fail('Error: Compilation failed.');
   }
   writeString(out, code);
   int jsBytesWritten = code.length;
   info('compiled $dartBytesRead bytes Dart -> $jsBytesWritten bytes JS '
-       + 'in ${relativize(cwd, out)}');
+       'in ${relativize(cwd, out)}');
   if (!explicitOut) {
     String input = uriPathToNative(arguments[0]);
     String output = relativize(cwd, out);
     print('Dart file $input compiled to JavaScript: $output');
   }
 }
 
 class AbortLeg {
   final message;
   AbortLeg(this.message);
@@ skipping 107 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.
     }
   }
 }