Refine duplicate arrow function parameter location handling

src/parsing/expression-classifier.h

 // Copyright 2015 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_EXPRESSION_CLASSIFIER_H
 #define V8_PARSING_EXPRESSION_CLASSIFIER_H
 
 #include "src/messages.h"
 #include "src/parsing/scanner.h"
 
@@ skipping 392 matching lines @@
     if (invalid_productions_ & (1 << kind)) {
       for (int i = reported_errors_begin_; i < reported_errors_end_; i++) {
         if (reported_errors_->at(i).kind == kind)
           return reported_errors_->at(i);
       }
       UNREACHABLE();
     }
     // We should only be looking for an error when we know that one has
     // been reported.  But we're not...  So this is to make sure we have
     // the same behaviour.
+    UNREACHABLE();
+
+    // Make MSVC happy by returning an error from this inaccessible path.
     static Error none;
     return none;
   }
 
   // Adds e to the end of the list of reported errors for this classifier.
   // It is expected that this classifier is the last one in the stack.
   V8_INLINE void Add(const Error& e) {
     DCHECK_EQ(reported_errors_end_, reported_errors_->length());
     reported_errors_->Add(e, zone_);
     reported_errors_end_++;
@@ skipping 40 matching lines @@
 };
 
 
 #undef ERROR_CODES
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_PARSING_EXPRESSION_CLASSIFIER_H