Reduce usage of .enclosingElement to get enclosing class.

lib/compiler/implementation/ssa/optimize.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.
 
 interface OptimizationPhase {
   String get name();
   void visitGraph(HGraph graph);
 }
 
 class SsaOptimizerTask extends CompilerTask {
@@ skipping 1173 matching lines @@
       other = node.right;
     } else if (node.right is HFieldGet) {
       field = node.right;
       other = node.left;
     }
     // Try to optimize the case where a field which is known to always
     // be an integer is compared with a constant number.
     if (other != null &&
         other.isConstantNumber() &&
         field.element != null &&
-        field.element.enclosingElement.isClass()) {
+        field.element.isMember()) {
       // Calculate the field type from the information available.  If
       // we have type information for the field and it contains NUMBER
       // we use it as a candidate for recompilation.
       Element fieldElement = field.element;
       HType fieldSettersType = backend.fieldSettersTypeSoFar(fieldElement);
       HType initializersType = backend.typeFromInitializersSoFar(fieldElement);
       HType fieldType = fieldSettersType.union(initializersType);
       HType type = HType.NUMBER.union(fieldType);
       if (type == HType.NUMBER) {
         handleFieldNumberOperation(field, fieldType);
@@ skipping 100 matching lines @@
       // this type for the field is still a strong signal
       // indicating the expected type of the field.
       field.propagatedType = type;
     } else {
       // If there are no invoked setters we know the type of
       // this field for sure.
       field.guaranteedType = type;
     }
   }
 }