Fix an ASSERT in the scanner

src/scanner.cc

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 165 matching lines @@
     // note: currently the following increment is necessary to avoid a
     // test-parser problem!
     pos_++;
     return static_cast<uc32>(-1);
   }
 }
 
 
 void TwoByteStringUTF16Buffer::PushBack(uc32 ch) {
   pos_--;
-  ASSERT(pos_ >= 0 && raw_data_[pos_] == ch);
+  ASSERT(pos_ >= Scanner::kCharacterLookaheadBufferSize);
+  ASSERT(raw_data_[pos_ - Scanner::kCharacterLookaheadBufferSize] == ch);
 }
 
 
 void TwoByteStringUTF16Buffer::SeekForward(int pos) {
   pos_ = pos;
 }
 
 
 // ----------------------------------------------------------------------------
 // Scanner
@@ skipping 768 matching lines @@
     }
     AddCharAdvance();
   }
   TerminateLiteral();
 
   next_.location.end_pos = source_pos() - 1;
   return true;
 }
 
 } }  // namespace v8::internal