Remove duplicated code from comma-separated Expression parsing

src/parsing/parser.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_H_
 #define V8_PARSING_PARSER_H_
 
 #include "src/ast/ast.h"
 #include "src/ast/scopes.h"
 #include "src/parsing/parser-base.h"
@@ skipping 861 matching lines @@
 
   // "null" return type creators.
   V8_INLINE static const AstRawString* EmptyIdentifier() { return nullptr; }
   V8_INLINE static Expression* EmptyExpression() { return nullptr; }
   V8_INLINE static Literal* EmptyLiteral() { return nullptr; }
   V8_INLINE static ObjectLiteralProperty* EmptyObjectLiteralProperty() {
     return nullptr;
   }
   V8_INLINE static FunctionLiteral* EmptyFunctionLiteral() { return nullptr; }
 
+  V8_INLINE static bool IsEmptyExpression(Expression* expr) {
+    return expr == nullptr;
+  }
+
   // Used in error return values.
   V8_INLINE static ZoneList<Expression*>* NullExpressionList() {
     return nullptr;
   }
 
   // Non-NULL empty string.
   V8_INLINE const AstRawString* EmptyIdentifierString() const {
     return ast_value_factory()->empty_string();
   }
 
@@ skipping 190 matching lines @@
   static const int kLiteralTypeSlot = 0;
   static const int kElementsSlot = 1;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(CompileTimeValue);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_PARSING_PARSER_H_