Implement part-of directive.

dart/lib/compiler/implementation/scanner/listener.dart

Index: dart/lib/compiler/implementation/scanner/listener.dart
diff --git a/dart/lib/compiler/implementation/scanner/listener.dart b/dart/lib/compiler/implementation/scanner/listener.dart
index 2017961c5a8ed5f4ebd4e522d21fd37284dceb12..55d6172eacd1df540d41828e9b2330e4e92bc9c4 100644
--- a/dart/lib/compiler/implementation/scanner/listener.dart
+++ b/dart/lib/compiler/implementation/scanner/listener.dart
@@ -691,7 +691,11 @@ class ElementListener extends Listener {
 
   void endPartOf(Token partKeyword, Token semicolon) {
     Expression name = popNode();
-    addLibraryTag(new PartOf(partKeyword, name));
+    addPartOfTag(new PartOf(partKeyword, name));
+  }
+
+  void addPartOfTag(PartOf tag) {
+    compilationUnitElement.setPartOf(tag, listener);
   }
 
   void endScriptTag(bool hasPrefix, Token beginToken, Token endToken) {
@@ -1104,6 +1108,10 @@ class NodeListener extends ElementListener {
     pushNode(tag);
   }
 
+  void addPartOfTag(PartOf tag) {
+    pushNode(tag);
+  }
+
   void endArgumentDefinitionTest(Token beginToken, Token endToken) {
     pushNode(new Send.prefix(popNode(), new Operator(beginToken)));
   }