[inspector] support for nested scheduled breaks

test/inspector/debugger/inspector-break-api.js

 // Copyright 2017 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.
 
 print("Checks breakProgram,(schedule|cancel)PauseOnNextStatement test API");
 
 InspectorTest.addScript(`
 function callBreakProgram() {
   breakProgram('reason', JSON.stringify({a: 42}));
 }
@@ skipping 19 matching lines @@
   function testBreakProgram(next) {
     Protocol.Runtime.evaluate({ expression: 'callBreakProgram()'})
       .then(next);
   },
 
   function testSchedulePauseOnNextStatement(next) {
     schedulePauseOnNextStatement('reason', JSON.stringify({a: 42}));
     Protocol.Runtime.evaluate({ expression: 'foo()//# sourceURL=expr1.js'})
       .then(() => Protocol.Runtime.evaluate({
         expression: 'foo()//# sourceURL=expr2.js'}))
+      .then(() => cancelPauseOnNextStatement())
       .then(next);
   },
 
   function testCancelPauseOnNextStatement(next) {
     schedulePauseOnNextStatement('reason', JSON.stringify({a: 42}));
     cancelPauseOnNextStatement();
     Protocol.Runtime.evaluate({ expression: 'foo()'})
       .then(next);
   }
 ]);