Change inference element invariants

pkg/compiler/lib/src/inferrer/locals_handler.dart

 // Copyright (c) 2013, 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 locals_handler;
 
 import 'dart:collection' show IterableMixin;
 
 import '../options.dart' show CompilerOptions;
 import '../elements/elements.dart';
@@ skipping 281 matching lines @@
       : locals = new VariableScope.topLevelCopyOf(other.locals),
         fieldScope = new FieldInitializationScope.from(other.fieldScope),
         captured = other.captured,
         capturedAndBoxed = other.capturedAndBoxed,
         tryBlock = other.tryBlock,
         types = other.types,
         inferrer = other.inferrer,
         options = other.options;
 
   TypeInformation use(Local local) {
+    assert(!(local is LocalElement && !local.isImplementation));
     if (capturedAndBoxed.containsKey(local)) {
       FieldElement field = capturedAndBoxed[local];
       return inferrer.typeOfMember(field);
     } else {
       if (captured.containsKey(local)) {
         inferrer.recordCapturedLocalRead(local);
       }
       return locals[local];
     }
   }
@@ skipping 233 matching lines @@
       if (newType != type) {
         locals[variable] = newType;
       }
     });
   }
 
   void updateField(Element element, TypeInformation type) {
     fieldScope.updateField(element, type);
   }
 }