Stop importing js_helper.dart explicitly in the core library.

lib/compiler/implementation/compiler.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.
 
 
 /**
  * If true, print a warning for each method that was resolved, but not
  * compiled.
  */
 const bool REPORT_EXCESS_RESOLUTION = false;
@@ skipping 346 matching lines @@
     closureClass = lookupSpecialClass(const SourceString('Closure'));
     dynamicClass = lookupSpecialClass(const SourceString('Dynamic_'));
     nullClass = lookupSpecialClass(const SourceString('Null'));
     types = new Types(this, dynamicClass);
     if (!coreLibValid) {
       cancel('core library does not contain required classes');
     }
   }
 
   void scanBuiltinLibraries() {
-    coreImplLibrary = scanBuiltinLibrary('coreimpl');
+    loadCoreImplLibrary();
     jsHelperLibrary = scanBuiltinLibrary('_js_helper');
     interceptorsLibrary = scanBuiltinLibrary('_interceptors');
 
+    // The core and coreimpl libraries were loaded and patched before
+    // jsHelperLibrary was initialized, so it wasn't imported into those
+    // two libraries during patching.
+    importHelperLibrary(coreLibrary);
+    importHelperLibrary(coreImplLibrary);
+    importHelperLibrary(interceptorsLibrary);
+
     addForeignFunctions(jsHelperLibrary);
     addForeignFunctions(interceptorsLibrary);
 
-    libraries['dart:core'] = coreLibrary;
-    libraries['dart:coreimpl'] = coreImplLibrary;
-
     assertMethod = jsHelperLibrary.find(const SourceString('assert'));
     identicalFunction = coreLibrary.find(const SourceString('identical'));
 
     initializeSpecialClasses();
   }
 
+  void loadCoreImplLibrary() {
+    Uri coreImplUri = new Uri.fromComponents(scheme: 'dart', path: 'coreimpl');
+    coreImplLibrary = scanner.loadLibrary(coreImplUri, null, coreImplUri);
+  }
+
+  void importHelperLibrary(LibraryElement library) {
+    if (jsHelperLibrary !== null) {
+      scanner.importLibrary(library, jsHelperLibrary, null);
+    }
+  }
+
   void importCoreLibrary(LibraryElement library) {
-    Uri coreUri = new Uri.fromComponents(scheme: 'dart', path: 'core');
     if (coreLibrary === null) {
+      Uri coreUri = new Uri.fromComponents(scheme: 'dart', path: 'core');
       coreLibrary = scanner.loadLibrary(coreUri, null, coreUri);
     }
     scanner.importLibrary(library,
                           coreLibrary,
                           null,
                           library.entryCompilationUnit);
   }
 
   void patchDartLibrary(LibraryElement library, String dartLibraryPath) {
     if (library.isPatched) return;
@@ skipping 439 matching lines @@
  * information in the generated error message.
  */
 bool invariant(Spannable spannable, var condition, {String message: null}) {
   // TODO(johnniwinther): Use [spannable] and [message] to provide better
   // information on assertion errors.
   if (condition is Function){
     condition = condition();
   }
   return spannable != null && condition;
 }