Revert "Revert "Allow patch files to add top-level declarations to the patched library.""

lib/compiler/implementation/scanner/class_element_parser.dart

 // Copyright (c) 2011, 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.
 
 class ClassElementParser extends PartialParser {
   ClassElementParser(Listener listener) : super(listener);
 
   Token parseClassBody(Token token) => fullParseClassBody(token);
 }
 
 class PartialClassElement extends ClassElement {
   final Token beginToken;
   final Token endToken;
   Node cachedNode;
 
   PartialClassElement(SourceString name,
                       Token this.beginToken,
                       Token this.endToken,
-                      CompilationUnitElement enclosing,
+                      Element enclosing,
                       int id)
-    : super(name, enclosing, id);
+      : super(name, enclosing, id);
 
   ClassNode parseNode(DiagnosticListener diagnosticListener) {
     if (cachedNode != null) return cachedNode;
     MemberListener listener = new MemberListener(diagnosticListener, this);
     Parser parser = new ClassElementParser(listener);
     Token token = parser.parseTopLevelDeclaration(beginToken);
     assert(token === endToken.next);
     cachedNode = listener.popNode();
     assert(listener.nodes.isEmpty());
     return cachedNode;
   }
 
   Token position() => beginToken;
 
   bool isInterface() => beginToken.stringValue === "interface";
+
+  PartialClassElement cloneTo(Element enclosing, DiagnosticListener listener) {
+    parseNode(listener);
+    PartialClassElement result =
+        new PartialClassElement(name, beginToken, endToken, enclosing, id);
+    cloneMembersTo(result, listener);
+    result.cachedNode = cachedNode;
+    return result;
+  }
 }
 
 class MemberListener extends NodeListener {
   final ClassElement enclosingElement;
 
   MemberListener(DiagnosticListener listener,
                  Element enclosingElement)
-    : this.enclosingElement = enclosingElement,
-      super(listener, enclosingElement.getCompilationUnit());
+      : this.enclosingElement = enclosingElement,
+        super(listener, enclosingElement.getCompilationUnit());
 
   bool isConstructorName(Node nameNode) {
     if (enclosingElement === null ||
         enclosingElement.kind != ElementKind.CLASS) {
       return false;
     }
     SourceString name;
     if (nameNode.asIdentifier() !== null) {
       name = nameNode.asIdentifier().source;
     } else {
@@ skipping 73 matching lines @@
   }
 
   void endInitializers(int count, Token beginToken, Token endToken) {
     pushNode(null);
   }
 
   void addMember(Element memberElement) {
     enclosingElement.addMember(memberElement, listener);
   }
 }