Fix some observatory analysis issues.

runtime/observatory/lib/src/cpu_profile/cpu_profile.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.
 
 part of cpu_profiler;
 
 abstract class CallTreeNode<NodeT extends M.CallTreeNode>
     implements M.CallTreeNode {
   final List<NodeT> children;
   final int count;
@@ skipping 827 matching lines @@
         return sleep();
       };
       try {
         clear();
         progress.add(0.0);
         if (profile == null) {
           return;
         }
 
         if ((owner != null) && (owner is Isolate)) {
-          isolate = owner as Isolate;
+          isolate = owner;
           isolate.resetCachedProfileData();
         }
 
         sampleCount = profile['sampleCount'];
         samplePeriod = profile['samplePeriod'];
         sampleRate = (Duration.MICROSECONDS_PER_SECOND / samplePeriod);
         stackDepth = profile['stackDepth'];
         timeSpan = profile['timeSpan'];
 
         num length = profile['codes'].length + profile['functions'].length;
@@ skipping 214 matching lines @@
   }
 
   int approximateMillisecondsForCount(count) {
     return (count * samplePeriod) ~/ Duration.MICROSECONDS_PER_MILLISECOND;
   }
 
   double approximateSecondsForCount(count) {
     return (count * samplePeriod) / Duration.MICROSECONDS_PER_SECOND;
   }
 }