Fix analyzer warnings in service tests

runtime/observatory/tests/service/evaluate_activation_test.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.
 // VMOptions=--compile-all --error_on_bad_type --error_on_bad_override
 
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
-import 'dart:async';
 
 import 'dart:math' as math;
 
 breakHere() {}
 
+use(dynamic v) => v;
+
 class C {
   var instVar = 1;
   static var classVar = 2;
 
   method(methodParam) {
     var methodTemp = 4;
+    use(methodTemp);
     [5].forEach((outerParam) {
       var outerTemp = 6;
+      use(outerTemp);
       [7].forEach((innerParam) {
         var innerTemp = 8;
+        use(innerTemp);
         breakHere();
       });
     });
   }
 
   static method2(methodParam) {
     var methodTemp = 4;
+    use(methodTemp);
     [5].forEach((outerParam) {
       var outerTemp = 6;
+      use(outerTemp);
       [7].forEach((innerParam) {
         var innerTemp = 8;
+        use(innerTemp);
         breakHere();
       });
     });
   }
 
   method3(methodParam) {
     var methodTemp = 4;
+    use(methodTemp);
     breakHere();
   }
 
   static var closureWithReturnedHome;
   method4(methodParam) {
     var methodTemp = 4;
+    use(methodTemp);
     [5].forEach((outerParam) {
       var outerTemp = 6;
+      use(outerTemp);
       closureWithReturnedHome = (innerParam) {
         var innerTemp = 8;
+        use(innerTemp);
         breakHere();
       };
     });
   }
 }
 
 testMethod(Isolate isolate) async {
+  // silence analyzer.
+  expect(math.sqrt(4), equals(2));
   Library rootLib = await isolate.rootLib.load();
   ServiceFunction function =
       rootLib.functions.singleWhere((f) => f.name == 'breakHere');
   Breakpoint bpt = await isolate.addBreakpointAtEntry(function);
   print("Breakpoint: $bpt");
   expect(bpt is Breakpoint, isTrue);  // I.e, not null.
 
   bool hitBreakpoint = false;
   var sub;
   sub = isolate.vm.events.stream.listen((ServiceEvent event) async {
@@ skipping 173 matching lines @@
 }
 
 var tests = [
   testMethod,
   testMethod2,
   testMethod3,
   testMethod4,
 ];
 
 main(args) => runIsolateTests(args, tests);