Reduce usage of .enclosingElement to get enclosing class.

lib/compiler/implementation/native_handler.dart

 // Copyright (c) 2012, 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.
 
 #library('native');
 #import('dart:uri');
 #import('leg.dart');
 #import('elements/elements.dart');
 #import('scanner/scannerlib.dart');
 #import('ssa/ssa.dart');
@@ skipping 170 matching lines @@
   FunctionElement element = builder.work.element;
   element.setNative();
   NativeEmitter nativeEmitter = builder.emitter.nativeEmitter;
   // If what we're compiling is a getter named 'typeName' and the native
   // class is named 'DOMType', we generate a call to the typeNameOf
   // function attached on the isolate.
   // The DOM classes assume that their 'typeName' property, which is
   // not a JS property on the DOM types, returns the type name.
   if (element.name == const SourceString('typeName')
       && element.isGetter()
-      && nativeEmitter.toNativeName(element.enclosingElement) == 'DOMType') {
+      && nativeEmitter.toNativeName(element.getEnclosingClass()) == 'DOMType') {
     Element methodElement =
         compiler.findHelper(const SourceString('getTypeNameOf'));
     HStatic method = new HStatic(methodElement);
     builder.add(method);
     builder.push(new HInvokeStatic(Selector.INVOCATION_1,
         <HInstruction>[method, builder.localsHandler.readThis()]));
     builder.close(new HReturn(builder.pop())).addSuccessor(builder.graph.exit);
   }
 
   HInstruction convertDartClosure(Element parameter, FunctionType type) {
@@ skipping 127 matching lines @@
                                       String parameters) {
   buffer.add("  if (Object.getPrototypeOf(this).hasOwnProperty");
   buffer.add("('$methodName')) {\n");
   buffer.add("  $code");
   buffer.add("  } else {\n");
   buffer.add("    return Object.prototype.$methodName.call(this");
   buffer.add(parameters == '' ? '' : ', $parameters');
   buffer.add(");\n");
   buffer.add("  }\n");
 }