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

src/parsing/parser-base.h

 // Copyright 2012 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.
 
 #ifndef V8_PARSING_PARSER_BASE_H
 #define V8_PARSING_PARSER_BASE_H
 
 #include "src/ast/scopes.h"
 #include "src/bailout-reason.h"
 #include "src/hashmap.h"
@@ skipping 2652 matching lines @@
         classifier->RecordAsyncArrowFormalParametersError(
             Scanner::Location(beg_pos, scanner()->location().end_pos),
             MessageTemplate::kAwaitBindingIdentifier);
 
         return this->ExpressionFromIdentifier(
             name, beg_pos, scanner()->location().end_pos, scope_, factory());
       }
       default:
         break;
     }
+
+    int await_pos = peek_position();
     Consume(Token::AWAIT);
 
     ExpressionT value = ParseUnaryExpression(classifier, CHECK_OK);
 
     classifier->RecordFormalParameterInitializerError(
         Scanner::Location(beg_pos, scanner()->location().end_pos),
         MessageTemplate::kAwaitExpressionFormalParameter);
-    return Traits::RewriteAwaitExpression(value, beg_pos);
+    return Traits::RewriteAwaitExpression(value, await_pos);
   } else {
     return this->ParsePostfixExpression(classifier, ok);
   }
 }
 
 
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParsePostfixExpression(ExpressionClassifier* classifier,
                                            bool* ok) {
@@ skipping 905 matching lines @@
     has_seen_constructor_ = true;
     return;
   }
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_PARSING_PARSER_BASE_H