[inspector] Refactor protocol-test.js

test/inspector/console/let-const-with-api.js

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+let {session, contextGroup, Protocol} = InspectorTest.start('Tests how let and const interact with command line api');
+
 Protocol.Runtime.evaluate({ expression: "let a = 42;" }).then(step2);
 
 function step2(response)
 {
   failIfError(response);
   InspectorTest.log("first \"let a = 1;\" result: wasThrown = " + !!response.result.exceptionDetails);
   Protocol.Runtime.evaluate({ expression: "let a = 239;" }).then(step3);
 }
 
 function step3(response)
@@ skipping 28 matching lines @@
     InspectorTest.completeTest();
 
   Protocol.Runtime.evaluate({ expression: method, includeCommandLineAPI: true }).then(checkMethod);
 }
 
 function failIfError(response)
 {
   if (response && response.error)
     InspectorTest.log("FAIL: " + JSON.stringify(response.error));
 }