Reduce usage of .enclosingElement to get enclosing class.

lib/compiler/implementation/namer.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.
 
 /**
  * Assigns JavaScript identifiers to Dart variables, class-names and members.
  */
 class Namer {
   final Compiler compiler;
 
@@ skipping 160 matching lines @@
 
   /**
    * Returns a preferred JS-id for the given top-level or static element.
    * The returned id is guaranteed to be a valid JS-id.
    */
   String _computeGuess(Element element) {
     assert(!element.isInstanceMember());
     LibraryElement lib = element.getLibrary();
     String name;
     if (element.isGenerativeConstructor()) {
-      if (element.name == element.enclosingElement.name) {
+      if (element.name == element.getEnclosingClass().name) {
         // Keep the class name for the class and not the factory.
         name = "${element.name.slowToString()}\$";
       } else {
         name = element.name.slowToString();
       }
     } else if (Elements.isStaticOrTopLevel(element)) {
-      if (element.enclosingElement != null &&
-          element.enclosingElement.isClass()) {
-        name = "${element.enclosingElement.name.slowToString()}_"
+      if (element.isMember()) {
+        ClassElement enclosingClass = element.getEnclosingClass();
+        name = "${enclosingClass.name.slowToString()}_"
                "${element.name.slowToString()}";
       } else {
         name = element.name.slowToString();
       }
     } else if (element.kind === ElementKind.LIBRARY) {
       name = LIBRARY_PREFIX;
     } else {
       name = element.name.slowToString();
     }
     // Prefix the name with '$' if it is reserved.
@@ skipping 82 matching lines @@
   }
 
   String safeName(String name) {
     if (jsReserved.contains(name) || name.startsWith('\$')) {
       name = "\$$name";
       assert(!jsReserved.contains(name));
     }
     return name;
   }
 }