dumpinfo: fix type error in checked mode

pkg/compiler/lib/src/dump_info.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 dump_info;
 
 import 'dart:convert'
     show HtmlEscape, JsonEncoder, StringConversionSink, ChunkedConversionSink;
 
 import 'elements/elements.dart';
@@ skipping 441 matching lines @@
         ..close();
     });
   }
 
   void dumpInfoJson(StringSink buffer) {
     JsonEncoder encoder = const JsonEncoder.withIndent('  ');
     Stopwatch stopwatch = new Stopwatch();
     stopwatch.start();
 
     // Recursively build links to function uses
-    Iterable<FunctionElement> functionElements =
+    Iterable<Element> functionElements =
         infoCollector._elementToInfo.keys.where((k) => k is FunctionElement);
     for (FunctionElement element in functionElements) {
       FunctionInfo info = infoCollector._elementToInfo[element];
       Iterable<Selection> uses = getRetaining(element);
       // Don't bother recording an empty list of dependencies.
       for (Selection selection in uses) {
         // Don't register dart2js builtin functions that are not recorded.
         Info useInfo = infoCollector._elementToInfo[selection.selectedElement];
         if (useInfo == null) continue;
         info.uses.add(new DependencyInfo(useInfo, '${selection.mask}'));
@@ skipping 26 matching lines @@
 
     ChunkedConversionSink<Object> sink = encoder.startChunkedConversion(
         new StringConversionSink.fromStringSink(buffer));
     sink.add(result.toJson());
     compiler.reportInfo(NO_LOCATION_SPANNABLE, MessageKind.GENERIC, {
       'text': "View the dumped .info.json file at "
           "https://dart-lang.github.io/dump-info-visualizer"
     });
   }
 }