Prevent duplicate entries in the bundled libraries

editor/tools/plugins/com.google.dart.tools.core_test/src/com/google/dart/tools/core/internal/model/SystemLibraryManagerProviderTest.java

Index: editor/tools/plugins/com.google.dart.tools.core_test/src/com/google/dart/tools/core/internal/model/SystemLibraryManagerProviderTest.java
===================================================================
--- editor/tools/plugins/com.google.dart.tools.core_test/src/com/google/dart/tools/core/internal/model/SystemLibraryManagerProviderTest.java	(revision 5968)
+++ editor/tools/plugins/com.google.dart.tools.core_test/src/com/google/dart/tools/core/internal/model/SystemLibraryManagerProviderTest.java	(working copy)
@@ -18,6 +18,7 @@
 import java.net.URI;
 import java.net.URISyntaxException;
 import java.util.Collection;
+import java.util.HashSet;
 
 public abstract class SystemLibraryManagerProviderTest extends TestCase {
 
@@ -59,6 +60,21 @@
     assertTrue(specs.contains("dart:uri"));
   }
 
+  public void test_SystemLibraryManagerProvider_getAllLibrarySpecs_no_duplicates() throws Exception {
+    EditorLibraryManager libraryManager = getLibraryManager();
+    Collection<String> specs = libraryManager.getAllLibrarySpecs();
+    Collection<String> visited = new HashSet<String>();
+    String actual = "";
+    for (String eachSpec : specs) {
+      if (visited.contains(eachSpec)) {
+        actual += eachSpec + ", ";
+      } else {
+        visited.add(eachSpec);
+      }
+    }
+    assertEquals("", actual);
+  }
+
   public void test_SystemLibraryManagerProvider_translateDoesNotExist() throws Exception {
     URI fullUri = new URI("dart://doesnotexist/some/file.dart");
     try {