Clear analyzer warning on Observatory

runtime/observatory/tests/service/get_native_allocation_samples_test.dart

 // Copyright (c) 2017, 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.
 // VMOptions=--error_on_bad_type --error_on_bad_override
 
-import 'package:observatory/cpu_profile.dart';
+import 'package:observatory/sample_profile.dart';
 import 'package:observatory/models.dart' as M;
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
 
 void verifyHelper(var root, bool exclusive) {
   if (root.children.length == 0) {
     return;
   }
 
@@ skipping 33 matching lines @@
   for (int i = 0; i < node.children.length; i++) {
     verifyHelper(node.children[i], exclusive);
   }
 }
 
 var tests = [
   // Verify inclusive tries.
   (VM vm) async {
     var response =
         await vm.invokeRpc('_getNativeAllocationSamples', {'tags': 'None'});
-    CpuProfile cpuProfile = new CpuProfile();
+    SampleProfile cpuProfile = new SampleProfile();
     await cpuProfile.load(vm, response);
     var codeTree = cpuProfile.loadCodeTree(M.ProfileTreeDirection.inclusive);
     var functionTree =
         cpuProfile.loadFunctionTree(M.ProfileTreeDirection.inclusive);
     verify(codeTree, false);
     verify(functionTree, false);
   },
   // Verify exclusive tries.
   (VM vm) async {
     var response =
         await vm.invokeRpc('_getNativeAllocationSamples', {'tags': 'None'});
-    CpuProfile cpuProfile = new CpuProfile();
+    SampleProfile cpuProfile = new SampleProfile();
     await cpuProfile.load(vm, response);
     var codeTreeExclusive =
         cpuProfile.loadCodeTree(M.ProfileTreeDirection.exclusive);
     var functionTreeExclusive =
         cpuProfile.loadFunctionTree(M.ProfileTreeDirection.exclusive);
     verify(codeTreeExclusive, true);
     verify(functionTreeExclusive, true);
   }
 ];
 
 main(args) async => runVMTests(args, tests);