Add a top-level node in the Files view to display the SDK libraries.

editor/tools/plugins/com.google.dart.tools.ui/src/com/google/dart/tools/ui/internal/filesview/FilesViewerComparator.java

 /*
  * Copyright (c) 2012, the Dart project authors.
  * 
  * Licensed under the Eclipse Public License v1.0 (the "License"); you may not use this file except
  * in compliance with the License. You may obtain a copy of the License at
  * 
  * http://www.eclipse.org/legal/epl-v10.html
  * 
  * Unless required by applicable law or agreed to in writing, software distributed under the License
  * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
  * or implied. See the License for the specific language governing permissions and limitations under
  * the License.
  */
 
 package com.google.dart.tools.ui.internal.filesview;
 
-import com.google.dart.tools.core.model.DartLibrary;
-
 import org.eclipse.core.filesystem.IFileStore;
+import org.eclipse.core.resources.IContainer;
+import org.eclipse.core.resources.IResource;
 import org.eclipse.jface.viewers.ViewerComparator;
 
 import java.util.Comparator;
 
 /**
  * Sorts files alphabetically.
  */
 public class FilesViewerComparator extends ViewerComparator {
-  private static final int DEFAULT_SORT = 0;
-  private static final int SYSTEM_LIBRARY = 1;
-  private static final int DIRECTORY_SORT = 2;
-  private static final int FILESTORE_SORT = 3;
+  private static final int DIRECTORY_SORT = 0;
+  private static final int RESOURCE_SORT = 1;
+  private static final int FILESTORE_SORT = 2;
+  private static final int DEFAULT_SORT = 3;
 
   public FilesViewerComparator() {
     super(new Comparator<String>() {
       @Override
       public int compare(String arg0, String arg1) {
         // If you do a standard case insensitive sort, strings starting
         // with underscores sort to the top, which is not desired.
         return arg0.toUpperCase().compareTo(arg1.toUpperCase());
       }
     });
   }
 
   @Override
   public int category(Object element) {
-    if (element instanceof DartLibrary) {
-      return SYSTEM_LIBRARY;
+    if (element instanceof IContainer) {
+      return DIRECTORY_SORT;
+    } else if (element instanceof IResource) {
+      return RESOURCE_SORT;
     } else if (element instanceof IFileStore) {
       IFileStore fileStore = (IFileStore) element;
       if (fileStore.fetchInfo().isDirectory()) {
         return DIRECTORY_SORT;
       } else {
         return FILESTORE_SORT;
       }
     } else {
       return DEFAULT_SORT;
     }
   }
 
 }