Use the new Base64 support from dart:convert in Observatory.

runtime/observatory/lib/src/service/object.dart

 // Copyright (c) 2014, 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.
 
 part of service;
 
 /// Helper function for canceling a Future<StreamSubscription>.
 Future cancelFutureSubscription(
     Future<StreamSubscription> subscriptionFuture) async {
   if (subscriptionFuture != null) {
@@ skipping 1953 matching lines @@
       nodeCount = map['nodeCount'];
     }
     if (map['count'] != null) {
       count = map['count'];
     }
     if (map['_debuggerSettings'] != null &&
         map['_debuggerSettings']['_exceptions'] != null) {
       exceptions = map['_debuggerSettings']['_exceptions'];
     }
     if (map['bytes'] != null) {
-      var bytes = decodeBase64(map['bytes']);
+      var bytes = BASE64.decode(map['bytes']);
       bytesAsString = UTF8.decode(bytes);
     }
     if (map['logRecord'] != null) {
       logRecord = map['logRecord'];
       logRecord['time'] =
           new DateTime.fromMillisecondsSinceEpoch(logRecord['time']);
       logRecord['level'] = _findLogLevel(logRecord['level']);
     }
   }
 
@@ skipping 421 matching lines @@
     oneByteFunction = map['_oneByteFunction'];
     twoByteFunction = map['_twoByteFunction'];
     externalOneByteFunction = map['_externalOneByteFunction'];
     externalTwoByteFunction = map['_externalTwoByteFunction'];
 
     nativeFields = map['_nativeFields'];
     fields = map['fields'];
     elements = map['elements'];
     associations = map['associations'];
     if (map['bytes'] != null) {
-      var bytes = decodeBase64(map['bytes']);
+      var bytes = BASE64.decode(map['bytes']);
       switch (map['kind']) {
         case "Uint8ClampedList":
           typedElements = bytes.buffer.asUint8ClampedList(); break;
         case "Uint8List":
           typedElements = bytes.buffer.asUint8List(); break;
         case "Uint16List":
           typedElements = bytes.buffer.asUint16List(); break;
         case "Uint32List":
           typedElements = bytes.buffer.asUint32List(); break;
         case "Uint64List":
@@ skipping 1595 matching lines @@
     var v = list[i];
     if ((v is ObservableMap) && _isServiceMap(v)) {
       list[i] = owner.getFromMap(v);
     } else if (v is ObservableList) {
       _upgradeObservableList(v, owner);
     } else if (v is ObservableMap) {
       _upgradeObservableMap(v, owner);
     }
   }
 }