Fix ExternalTwobyteStringUtf16CharacterStream::PushBack(kEndOfInput)

src/parsing/scanner-character-streams.h

 // Copyright 2011 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_SCANNER_CHARACTER_STREAMS_H_
 #define V8_PARSING_SCANNER_CHARACTER_STREAMS_H_
 
 #include "src/handles.h"
 #include "src/parsing/scanner.h"
 #include "src/vector.h"
@@ skipping 140 matching lines @@
 // UTF16 buffer to read characters from an external string.
 class ExternalTwoByteStringUtf16CharacterStream: public Utf16CharacterStream {
  public:
   ExternalTwoByteStringUtf16CharacterStream(Handle<ExternalTwoByteString> data,
                                             int start_position,
                                             int end_position);
   ~ExternalTwoByteStringUtf16CharacterStream() override;
 
   void PushBack(uc32 character) override {
     DCHECK(buffer_cursor_ > raw_data_);
-    buffer_cursor_--;
     pos_--;
+    if (character != kEndOfInput) {
+      buffer_cursor_--;
+    }
   }
 
   bool SetBookmark() override;
   void ResetToBookmark() override;
 
  protected:
   size_t SlowSeekForward(size_t delta) override {
     // Fast case always handles seeking.
     return 0;
   }
   bool ReadBlock() override {
     // Entire string is read at start.
     return false;
   }
   Handle<ExternalTwoByteString> source_;
   const uc16* raw_data_;  // Pointer to the actual array of characters.
 
  private:
   static const size_t kNoBookmark = -1;
 
   size_t bookmark_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_PARSING_SCANNER_CHARACTER_STREAMS_H_