Fix custom formatter setup, take 2

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

Index: pkg/dev_compiler/lib/js/legacy/dart_library.js
diff --git a/pkg/dev_compiler/lib/js/legacy/dart_library.js b/pkg/dev_compiler/lib/js/legacy/dart_library.js
index 4901310d7dc19511a577280266e389a8e4c13afd..89549ae240d6475f998a2f371ab4fc99a8d71436 100644
--- a/pkg/dev_compiler/lib/js/legacy/dart_library.js
+++ b/pkg/dev_compiler/lib/js/legacy/dart_library.js
@@ -153,7 +153,6 @@ dart_library =
   dart_library.library = library;
 
   function import_(libraryName) {
-    bootstrap();
     let loader = libraries.get(libraryName);
     // TODO(vsm): A user might call this directly from JS (as we do in tests).
     // We may want a different error type.
@@ -169,11 +168,11 @@ dart_library =
     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.
-    dart_sdk._debugger.registerDevtoolsFormatter();
-
     if (!_currentIsolate) {
+      // This import is only needed for chrome debugging. We should provide an
+      // option to compile without it.
+      dart_sdk._debugger.registerDevtoolsFormatter();
+
       // Create isolate.
       _currentIsolate = true;
       dart_sdk._isolate_helper.startRootIsolate(() => {}, []);
@@ -183,11 +182,5 @@ dart_library =
   }
   dart_library.start = start;
 
-  let _bootstrapped = false;
-  function bootstrap() {
-    if (_bootstrapped) return;
-    _bootstrapped = true;
-  }
-
 })(dart_library);
 }