Change inference element invariants

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 ChunkedConversionSink, JsonEncoder, StringConversionSink;
 
 import 'package:dart2js_info/info.dart';
@@ skipping 245 matching lines @@
     FunctionModifiers modifiers = new FunctionModifiers(
         isStatic: element.isStatic,
         isConst: element.isConst,
         isFactory: element.isFactoryConstructor,
         isExternal: element.isPatched);
     String code = compiler.dumpInfoTask.codeOf(element);
 
     String returnType = null;
     List<ParameterInfo> parameters = <ParameterInfo>[];
     if (element.hasFunctionSignature) {
-      FunctionSignature signature = element.functionSignature;
+      FunctionElement implementation = element.implementation;
+      FunctionSignature signature = implementation.functionSignature;
       signature.forEachParameter((parameter) {
         parameters.add(new ParameterInfo(parameter.name,
             '${_resultOfParameter(parameter).type}', '${parameter.node.type}'));
       });
       returnType = '${element.type.returnType}';
     }
 
     MethodElement method;
     if (element is LocalFunctionElement) {
       method = element.callMethod;
@@ skipping 341 matching lines @@
 
     ChunkedConversionSink<Object> sink = encoder.startChunkedConversion(
         new StringConversionSink.fromStringSink(buffer));
     sink.add(new AllInfoJsonCodec().encode(result));
     compiler.reporter.reportInfo(NO_LOCATION_SPANNABLE, MessageKind.GENERIC, {
       'text': "View the dumped .info.json file at "
           "https://dart-lang.github.io/dump-info-visualizer"
     });
   }
 }