More strong mode changes to analysis_server

pkg/analysis_server/benchmark/integration/instrumentation_input_converter.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 input.transformer.instrumentation;
 
 import 'dart:convert';
 
 import 'package:analyzer/instrumentation/instrumentation.dart';
 import 'package:analyzer/src/generated/java_engine.dart';
@@ skipping 78 matching lines @@
     }
     if (codesSeen.add(opCode)) {
       logger.log(
           Level.WARNING, 'Ignored instrumentation op code: $opCode\n  $line');
     }
     return null;
   }
 
   Map<String, dynamic> decodeJson(String line, String text) {
     try {
-      return JSON.decode(text);
+      return asMap(JSON.decode(text));
     } catch (e, s) {
       throw new AnalysisException(
           'Failed to decode JSON: $text\n$line', new CaughtException(e, s));
     }
   }
 
   /**
    * Determine if the given line is from an instrumentation file.
    * For example:
    * `1433175833005:Ver:1421765742287333878467:org.dartlang.dartplugin:0.0.0:1.6.2:1.11.0-edge.131698`
@@ skipping 29 matching lines @@
         sb.writeCharCode(code);
       }
       ++index;
     }
     if (sb.isNotEmpty) {
       fields.add(sb.toString());
     }
     return fields;
   }
 }