Record 'implements' keyword for class declaration nodes.

lib/compiler/implementation/scanner/listener.dart

Index: lib/compiler/implementation/scanner/listener.dart
diff --git a/lib/compiler/implementation/scanner/listener.dart b/lib/compiler/implementation/scanner/listener.dart
index 7d18d4d8ed3ea36f354eb1bb7fb119a0ae8c23ac..79f6cd595a24d552932272a359bbeeedeedc302f 100644
--- a/lib/compiler/implementation/scanner/listener.dart
+++ b/lib/compiler/implementation/scanner/listener.dart
@@ -898,7 +898,7 @@ class NodeListener extends ElementListener {
                            Token endToken) {
     NodeList body = popNode();
     NodeList interfaces =
-        makeNodeList(interfacesCount, implementsKeyword, null, ",");
+        makeNodeList(interfacesCount, null, null, ",");
     TypeAnnotation supertype = popNode();
     NodeList typeParameters = popNode();
     Identifier name = popNode();
@@ -919,8 +919,7 @@ class NodeListener extends ElementListener {
                     Token extendsKeyword, Token endToken) {
     NodeList body = popNode();
     TypeAnnotation defaultClause = popNode();
-    NodeList supertypes = makeNodeList(supertypeCount, extendsKeyword,
-                                       null, ',');
+    NodeList supertypes = makeNodeList(supertypeCount, null, null, ',');
     NodeList typeParameters = popNode();
     Identifier name = popNode();
     pushNode(new ClassNode(name, typeParameters, null, supertypes,