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

lib/compiler/implementation/scanner/class_element_parser.dart

Index: lib/compiler/implementation/scanner/class_element_parser.dart
diff --git a/lib/compiler/implementation/scanner/class_element_parser.dart b/lib/compiler/implementation/scanner/class_element_parser.dart
index 74e0a76f0d0452625543354b2e9a36a866c8f551..46012f3044f79cff64dc47f8be313d4d7ea47c38 100644
--- a/lib/compiler/implementation/scanner/class_element_parser.dart
+++ b/lib/compiler/implementation/scanner/class_element_parser.dart
@@ -18,7 +18,7 @@ class PartialClassElement extends ClassElement {
                       Token this.endToken,
                       CompilationUnitElement enclosing,
                       int id)
-    : super(name, enclosing, id);
+      : super(name, enclosing, id);
 
   ClassNode parseNode(DiagnosticListener diagnosticListener) {
     if (cachedNode != null) return cachedNode;
@@ -34,6 +34,17 @@ class PartialClassElement extends ClassElement {
   Token position() => beginToken;
 
   bool isInterface() => beginToken.stringValue === "interface";
+
+  PartialClassElement cloneTo(CompilationUnitElement enclosing,
+                              DiagnosticListener listener) {
+    parseNode(listener);
+    PartialClassElement result =
+        new PartialClassElement(name, beginToken, endToken, enclosing, id);
+    cloneMembersTo(result, listener);
+    result.cachedNode = cachedNode;
+    result.scriptOverride = getScript();
+    return result;
+  }
 }
 
 class MemberListener extends NodeListener {
@@ -41,8 +52,8 @@ class MemberListener extends NodeListener {
 
   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 ||