[inspector] Refactor protocol-test.js

test/inspector/debugger/stepping-after-get-possible-breakpoints.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.
 
-InspectorTest.addScript(`
+let {session, contextGroup, Protocol} = InspectorTest.start('Tests that stepping works after calling getPossibleBreakpoints');
+
+contextGroup.addScript(`
 function boo() {}
 boo();
 function foo() {}
 //# sourceURL=foo.js`);
 
 Protocol.Debugger.onPaused((message) => {
   InspectorTest.logMessage(message.params.callFrames[0].functionName || "(top)");
   Protocol.Debugger.stepInto();
 });
 var scriptId;
 Protocol.Debugger.onScriptParsed(message => {
   if (message.params.url === 'foo.js')
     scriptId = message.params.scriptId;
 });
 Protocol.Debugger.enable()
   .then(() => Protocol.Debugger.getPossibleBreakpoints({start: {scriptId, lineNumber:0,columnNumber:0}}))
   .then(() => InspectorTest.log('-- call boo:'))
   .then(() => Protocol.Runtime.evaluate({ expression: 'debugger; boo();'}))
   .then(() => InspectorTest.log('-- call foo:'))
   .then(() => Protocol.Runtime.evaluate({ expression: 'debugger; foo();'}))
   .then(InspectorTest.completeTest);