[debug] implement intuitive semantics for stepping over await call.

test/mjsunit/harmony/async-function-debug-scopes.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.
 
 // Flags: --harmony-async-await --expose-debug-as debug
 
 var Debug = debug.Debug;
 
 var AsyncFunction = (async function() {}).constructor;
 
@@ skipping 483 matching lines @@
   for (var i = 0; i < scopes.length && i < length; i++) {
     var scope = fast_all_scopes[length - i - 1];
     assertTrue(scope.isScope());
     assertEquals(scopes[scopes.length - i - 1], scope.scopeType());
   }
 }
 
 // Check that the scope chain contains the expected types of scopes.
 function CheckScopeChain(scopes, exec_state) {
   var all_scopes = exec_state.frame().allScopes();
-  assertEquals(scopes.length, exec_state.frame().scopeCount());
   assertEquals(
       scopes.length, all_scopes.length, "FrameMirror.allScopes length");
   for (var i = 0; i < scopes.length; i++) {
     var scope = exec_state.frame().scope(i);
     assertTrue(scope.isScope());
     assertEquals(scopes[i], scope.scopeType());
     assertScopeMirrorEquals(all_scopes[i], scope);
 
     // Check the global object when hitting the global scope.
     if (scopes[i] == debug.ScopeType.Global) {
@@ skipping 93 matching lines @@
     assertTrue(response.body.object.ref < 0);
   } else {
     assertTrue(response.body.object.ref >= 0);
   }
   var found = false;
   for (var i = 0; i < response.refs.length && !found; i++) {
     found = response.refs[i].handle == response.body.object.ref;
   }
   assertTrue(found, "Scope object " + response.body.object.ref + " not found");
 }