Fix Scanner::PushBack for surrogate code points.

src/parsing/scanner.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.
 
 // Features shared by parsing and pre-parsing scanners.
 
 #ifndef V8_PARSING_SCANNER_H_
 #define V8_PARSING_SCANNER_H_
 
 #include "src/allocation.h"
@@ skipping 570 matching lines @@
       uc32 c1 = source_->Advance();
       if (!unibrow::Utf16::IsTrailSurrogate(c1)) {
         source_->PushBack(c1);
       } else {
         c0_ = unibrow::Utf16::CombineSurrogatePair(c0_, c1);
       }
     }
   }
 
   void PushBack(uc32 ch) {
-    if (ch > static_cast<uc32>(unibrow::Utf16::kMaxNonSurrogateCharCode)) {
+    if (c0_ > static_cast<uc32>(unibrow::Utf16::kMaxNonSurrogateCharCode)) {
       source_->PushBack(unibrow::Utf16::TrailSurrogate(c0_));
       source_->PushBack(unibrow::Utf16::LeadSurrogate(c0_));
     } else {
       source_->PushBack(c0_);
     }
     c0_ = ch;
   }
 
   inline Token::Value Select(Token::Value tok) {
     Advance();
@@ skipping 191 matching lines @@
   bool allow_harmony_exponentiation_operator_;
 
   MessageTemplate::Template scanner_error_;
   Location scanner_error_location_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_PARSING_SCANNER_H_