Implement proper scoping for "this" in arrow functions

src/preparser.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_PREPARSER_H
 #define V8_PREPARSER_H
 
 #include "src/v8.h"
 
 #include "src/bailout-reason.h"
@@ skipping 1001 matching lines @@
   bool AllowsLazyCompilation() const { return false; }
 
   void set_start_position(int position) {}
   void set_end_position(int position) {}
 
   bool IsDeclared(const PreParserIdentifier& identifier) const { return false; }
   void DeclareParameter(const PreParserIdentifier& identifier, VariableMode) {}
   void RecordArgumentsUsage() {}
   void RecordSuperPropertyUsage() {}
   void RecordSuperConstructorCallUsage() {}
-  void RecordThisUsage() {}
 
   // Allow scope->Foo() to work.
   PreParserScope* operator->() { return this; }
 
  private:
   ScopeType scope_type_;
   StrictMode strict_mode_;
 };
 
 
@@ skipping 815 matching lines @@
   //   ClassLiteral
   //   '(' Expression ')'
   //   TemplateLiteral
 
   int pos = peek_position();
   ExpressionT result = this->EmptyExpression();
   Token::Value token = peek();
   switch (token) {
     case Token::THIS: {
       Consume(Token::THIS);
-      scope_->RecordThisUsage();
       result = this->ThisExpression(scope_, factory());
       break;
     }
 
     case Token::NULL_LITERAL:
     case Token::TRUE_LITERAL:
     case Token::FALSE_LITERAL:
     case Token::NUMBER:
       Next();
       result = this->ExpressionFromLiteral(token, pos, scanner(), factory());
@@ skipping 1192 matching lines @@
       DCHECK(IsAccessorAccessorConflict(old_type, type));
       // Both accessors of the same type.
       parser()->ReportMessage("accessor_get_set");
     }
     *ok = false;
   }
 }
 } }  // v8::internal
 
 #endif  // V8_PREPARSER_H