Split js interop registration into library/class/member elements

pkg/compiler/lib/src/js_backend/frequency_namer.dart

 // Copyright (c) 2015, 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.namer;
 
 class FrequencyBasedNamer extends Namer
     with _MinifiedFieldNamer, _MinifiedOneShotInterceptorNamer
     implements jsAst.TokenFinalizer {
   _FieldNamingRegistry fieldRegistry;
@@ skipping 46 matching lines @@
     String proposed = _generateFreshStringForName(proposedName, scope,
         sanitizeForNatives: sanitizeForNatives,
         sanitizeForAnnotations: sanitizeForAnnotations);
 
     TokenName name = new TokenName(tokenScope, proposed);
     tokens.add(name);
     return name;
   }
 
   @override
-  jsAst.Name instanceFieldPropertyName(Element element) {
+  jsAst.Name instanceFieldPropertyName(FieldElement element) {
     jsAst.Name proposed = _minifiedInstanceFieldPropertyName(element);
     if (proposed != null) {
       return proposed;
     }
     return super.instanceFieldPropertyName(element);
   }
 
   @override
   void finalizeTokens() {
     int compareReferenceCount(TokenName a, TokenName b) {
@@ skipping 55 matching lines @@
     String proposal;
     do {
       proposal = new String.fromCharCodes(_nextName);
       _incrementName();
     } while (MinifyNamer._hasBannedPrefix(proposal) ||
         illegalNames.contains(proposal));
 
     return proposal;
   }
 }