Resolve some static warnings.

pkg/compiler/lib/src/js_backend/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.
 
 part of js_backend;
 
 /**
  * Assigns JavaScript identifiers to Dart variables, class-names and members.
  *
  * Names are generated through three stages:
@@ skipping 767 matching lines @@
       return new StringBackedName(backend.getFixedBackendName(element));
     }
 
     // Some elements, like e.g. instances of BoxFieldElement are special.
     // They are created with a unique and safe name for the element model.
     // While their name is unique, it is not very readable. So we try to
     // preserve the original, proposed name.
     // However, as boxes are not really instances of classes, the usual naming
     // scheme that tries to avoid name clashes with super classes does not
     // apply. So we can directly grab a name.
-    if (element is JSEntity) {
+    Entity asEntity = element;
+    if (asEntity is JSEntity) {
       return _disambiguateInternalMember(element,
-                                         () => element.declaredEntity.name);
+                                         () => asEntity.declaredEntity.name);
     }
 
     // If the name of the field might clash with another field,
     // use a mangled field name to avoid potential clashes.
     // Note that if the class extends a native class, that native class might
     // have fields with fixed backend names, so we assume the worst and always
     // mangle the field names of classes extending native classes.
     // Methods on such classes are stored on the interceptor, not the instance,
     // so only fields have the potential to clash with a native property name.
     ClassWorld classWorld = compiler.world;
@@ skipping 204 matching lines @@
   /// This is used as the property name for fields, type variables,
   /// constructor bodies, and super-accessors.
   ///
   /// The resulting name is unique within the instance-member namespace.
   jsAst.Name _disambiguateInternalMember(Element element,
                                          String proposeName()) {
     jsAst.Name newName = internalInstanceMembers[element];
     if (newName == null) {
       String name = proposeName();
 
-      if (element is PrivatelyNamedJSEntity) {
-        NamingScope scope = _getPrivateScopeFor(element);
+      Entity asEntity = element;
+      if (asEntity is PrivatelyNamedJSEntity) {
+        NamingScope scope = _getPrivateScopeFor(asEntity);
         newName = getFreshName(scope, name,
                                sanitizeForAnnotations: true,
                                sanitizeForNatives: false);
         internalInstanceMembers[element] = newName;
       } else {
         bool mayClashNative =
             _isUserClassExtendingNative(element.enclosingClass);
         newName = getFreshName(instanceScope, name,
                                sanitizeForAnnotations: true,
                                sanitizeForNatives: mayClashNative);
@@ skipping 1008 matching lines @@
   String suggestName(String original) => _suggestedNames[original];
   void addSuggestion(String original, String suggestion) {
     assert(!_suggestedNames.containsKey(original));
     _suggestedNames[original] = suggestion;
   }
   bool hasSuggestion(String original) => _suggestedNames.containsKey(original);
   bool isSuggestion(String candidate) {
     return _suggestedNames.containsValue(candidate);
   }
 }