[parser,ast] Simplify MarkExpressionAsAssigned.

src/parsing/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_PARSING_PREPARSER_H
 #define V8_PARSING_PREPARSER_H
 
 #include "src/ast/scopes.h"
 #include "src/parsing/parser-base.h"
 
@@ skipping 1180 matching lines @@
   V8_INLINE static void PushVariableName(PreParserIdentifier id) {}
   V8_INLINE void PushPropertyName(PreParserExpression expression) {}
   V8_INLINE void PushEnclosingName(PreParserIdentifier name) {}
   V8_INLINE static void AddFunctionForNameInference(
       PreParserExpression expression) {}
   V8_INLINE static void InferFunctionName() {}
 
   V8_INLINE static void CheckAssigningFunctionLiteralToProperty(
       PreParserExpression left, PreParserExpression right) {}
 
-  V8_INLINE static PreParserExpression MarkExpressionAsAssigned(
+  V8_INLINE static void MarkExpressionAsAssigned(
       PreParserExpression expression) {
     // TODO(marja): To be able to produce the same errors, the preparser needs
     // to start tracking which expressions are variables and which are assigned.
-    return expression;
   }
 
   V8_INLINE bool ShortcutNumericLiteralBinaryExpression(PreParserExpression* x,
                                                         PreParserExpression y,
                                                         Token::Value op,
                                                         int pos) {
     return false;
   }
 
   V8_INLINE PreParserExpression BuildUnaryExpression(
@@ skipping 335 matching lines @@
     function_state_->NextMaterializedLiteralIndex();
     function_state_->NextMaterializedLiteralIndex();
   }
   return EmptyExpression();
 }
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_PARSING_PREPARSER_H