Fix custom formatter setup

pkg/dev_compiler/lib/js/legacy/dart_library.js

 // Copyright (c) 2015, 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.
 
 /* This file defines the module loader for the dart runtime.
 */
 var dart_library;
 if (!dart_library) {
 dart_library =
   typeof module != "undefined" && module.exports || {};
@@ skipping 151 matching lines @@
   }
   dart_library.import = import_;
 
   var _currentIsolate = false;
 
   function start(moduleName, libraryName) {
     if (libraryName == null) libraryName = moduleName;
     let library = import_(moduleName)[libraryName];
     let dart_sdk = import_('dart_sdk');
 
+    // This import is only needed for chrome debugging. We should provide an
+    // option to compile without it.

[Jacob, 2017/03/09 02:59:07]

you should make sure registerDevtoolsFormatter isn't called multiple times.

+    dart_sdk._debugger.registerDevtoolsFormatter();
+
     if (!_currentIsolate) {
       // Create isolate.
       _currentIsolate = true;
       dart_sdk._isolate_helper.startRootIsolate(() => {}, []);
     }
 
     library.main();
   }
   dart_library.start = start;
 
   let _bootstrapped = false;

[Jacob, 2017/03/09 02:59:07]

with this tweak the bootstrap method is now a no op. remove?

   function bootstrap() {
     if (_bootstrapped) return;
     _bootstrapped = true;
-
-    // This import is only needed for chrome debugging. We should provide an
-    // option to compile without it.
-    dart_sdk._debugger.registerDevtoolsFormatter();

[vsm, 2017/03/09 02:54:07]

dart_sdk isn't defined here - breaking internal tests

   }
 
 })(dart_library);
 }