More strong mode fixes for analyzer

pkg/analyzer/lib/src/summary/summarize_elements.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.
 
 library serialization.elements;
 
 import 'dart:convert';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
@@ skipping 835 matching lines @@
       b.uri = importElement.uri;
       b.uriOffset = importElement.uriOffset;
       b.uriEnd = importElement.uriEnd;
     }
     return b;
   }
 
   /**
    * Serialize the given [label], creating an [UnlinkedLabelBuilder].
    */
-  UnlinkedLabelBuilder serializeLabel(LabelElementImpl label) {
+  UnlinkedLabelBuilder serializeLabel(LabelElement label) {
+    LabelElementImpl labelImpl = label as LabelElementImpl;
     UnlinkedLabelBuilder b = new UnlinkedLabelBuilder();
-    b.name = label.name;
-    b.nameOffset = label.nameOffset;
-    b.isOnSwitchMember = label.isOnSwitchMember;
-    b.isOnSwitchStatement = label.isOnSwitchStatement;
+    b.name = labelImpl.name;
+    b.nameOffset = labelImpl.nameOffset;
+    b.isOnSwitchMember = labelImpl.isOnSwitchMember;
+    b.isOnSwitchStatement = labelImpl.isOnSwitchStatement;
     return b;
   }
 
   /**
    * Serialize the given [parameter] into an [UnlinkedParam].
    */
   UnlinkedParamBuilder serializeParam(ParameterElement parameter,
       [Element context]) {
     context ??= parameter;
     UnlinkedParamBuilder b = new UnlinkedParamBuilder();
@@ skipping 749 matching lines @@
       exportNames.add(new LinkedExportNameBuilder(
           name: name,
           dependency: serializeDependency(dependentLibrary),
           unit: unit,
           kind: kind));
     }
     pb.exportNames = exportNames;
     return pb;
   }
 }