Fix some observatory analysis issues.

runtime/observatory/lib/src/repositories/sample_profile.dart

 // Copyright (c) 2016, 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 repositories;
 
 String _tagToString(M.SampleProfileTag tag) {
   switch (tag) {
     case M.SampleProfileTag.userVM:
       return 'UserVM';
@@ skipping 52 matching lines @@
       }
 
       var response;
       if (type == M.SampleProfileType.cpu) {
         response = cls != null
             ? await cls.getAllocationSamples(_tagToString(tag))
             : await owner
                 .invokeRpc('_getCpuProfile', {'tags': _tagToString(tag)});
       } else if (type == M.SampleProfileType.memory) {
         assert(owner is M.VM);
-        M.VM vm = owner as M.VM;
         response = await owner.invokeRpc(
             '_getNativeAllocationSamples', {'tags': _tagToString(tag)});
       } else {
         throw new Exception('Unknown M.SampleProfileType: $type');
       }
 
       _fetchingTime.stop();
       _loadingTime.start();
       _status = M.SampleProfileLoadingStatus.loading;
       _triggerOnProgress();
@@ skipping 94 matching lines @@
     assert(forceFetch != null);
     if ((_last != null) && !forceFetch) {
       _last.reuse();
     } else {
       _last = new SampleProfileLoadingProgress(vm, t, false,
           type: M.SampleProfileType.memory);
     }
     return _last.onProgress;
   }
 }