Revert "Rewind additional parser state when reinterpreting arrow arguments"

src/preparser.h

Index: src/preparser.h
diff --git a/src/preparser.h b/src/preparser.h
index 06de6ebe2e4ccb7dca0a7f84f1d47146e549f484..517403d34733eba81ea86c7bedd38162feded389 100644
--- a/src/preparser.h
+++ b/src/preparser.h
@@ -114,8 +114,6 @@ class ParserBase : public Traits {
   }
 
  protected:
-  friend class Traits::Type::Checkpoint;
-
   enum AllowEvalOrArgumentsAsIdentifier {
     kAllowEvalOrArguments,
     kDontAllowEvalOrArguments
@@ -126,8 +124,6 @@ class ParserBase : public Traits {
     PARSE_EAGERLY
   };
 
-  class ParserCheckpoint;
-
   // ---------------------------------------------------------------------------
   // FunctionState and BlockState together implement the parser's scope stack.
   // The parser's current scope is in scope_. BlockState and FunctionState
@@ -223,38 +219,6 @@ class ParserBase : public Traits {
     typename Traits::Type::Factory factory_;
 
     friend class ParserTraits;
-    friend class ParserCheckpoint;
-  };
-
-  // Annoyingly, arrow functions first parse as comma expressions, then when we
-  // see the => we have to go back and reinterpret the arguments as being formal
-  // parameters.  To do so we need to reset some of the parser state back to
-  // what it was before the arguments were first seen.
-  class ParserCheckpoint : public Traits::Type::Checkpoint {
-   public:
-    template <typename Parser>
-    explicit ParserCheckpoint(Parser* parser)
-        : Traits::Type::Checkpoint(parser) {
-      function_state_ = parser->function_state_;
-      next_materialized_literal_index_ =
-          function_state_->next_materialized_literal_index_;
-      next_handler_index_ = function_state_->next_handler_index_;
-      expected_property_count_ = function_state_->expected_property_count_;
-    }
-
-    void Restore() {
-      Traits::Type::Checkpoint::Restore();
-      function_state_->next_materialized_literal_index_ =
-          next_materialized_literal_index_;
-      function_state_->next_handler_index_ = next_handler_index_;
-      function_state_->expected_property_count_ = expected_property_count_;
-    }
-
-   private:
-    FunctionState* function_state_;
-    int next_materialized_literal_index_;
-    int next_handler_index_;
-    int expected_property_count_;
   };
 
   class ParsingModeScope BASE_EMBEDDED {
@@ -1057,14 +1021,6 @@ class PreParserFactory {
 };
 
 
-class PreParserCheckpoint BASE_EMBEDDED {
- public:
-  template <typename Parser>
-  explicit PreParserCheckpoint(Parser* parser) {}
-  void Restore() {}
-};
-
-
 class PreParser;
 
 class PreParserTraits {
@@ -1077,7 +1033,6 @@ class PreParserTraits {
     // Used by FunctionState and BlockState.
     typedef PreParserScope Scope;
     typedef PreParserScope ScopePtr;
-    typedef PreParserCheckpoint Checkpoint;
 
     // PreParser doesn't need to store generator variables.
     typedef void GeneratorVariable;
@@ -2051,12 +2006,10 @@ ParserBase<Traits>::ParseAssignmentExpression(bool accept_IN, bool* ok) {
   }
 
   if (fni_ != NULL) fni_->Enter();
-  ParserCheckpoint checkpoint(this);
   ExpressionT expression =
       this->ParseConditionalExpression(accept_IN, CHECK_OK);
 
   if (allow_arrow_functions() && peek() == Token::ARROW) {
-    checkpoint.Restore();
     expression = this->ParseArrowFunctionLiteral(lhs_location.beg_pos,
                                                  expression, CHECK_OK);
     return expression;