Implement a 'trial parse' step, that will abort pre-parsing excessively

src/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_SCANNER_CHARACTER_STREAMS_H_
 #define V8_SCANNER_CHARACTER_STREAMS_H_
 
 #include "src/scanner.h"
 
 namespace v8 {
@@ skipping 25 matching lines @@
 };
 
 
 // Generic string stream.
 class GenericStringUtf16CharacterStream: public BufferedUtf16CharacterStream {
  public:
   GenericStringUtf16CharacterStream(Handle<String> data, size_t start_position,
                                     size_t end_position);
   virtual ~GenericStringUtf16CharacterStream();
 
+  virtual bool SetBookmark();
+  virtual void ResetToBookmark();
+
  protected:
   virtual size_t BufferSeekForward(size_t delta);
   virtual size_t FillBuffer(size_t position);
 
   Handle<String> string_;
   size_t length_;
+  size_t bookmark_;
 };
 
 
 // Utf16 stream based on a literal UTF-8 string.
 class Utf8ToUtf16CharacterStream: public BufferedUtf16CharacterStream {
  public:
   Utf8ToUtf16CharacterStream(const byte* data, size_t length);
   virtual ~Utf8ToUtf16CharacterStream();
 
   static size_t CopyChars(uint16_t* dest, size_t length, const byte* src,
@@ skipping 60 matching lines @@
                                             int start_position,
                                             int end_position);
   virtual ~ExternalTwoByteStringUtf16CharacterStream();
 
   virtual void PushBack(uc32 character) {
     DCHECK(buffer_cursor_ > raw_data_);
     buffer_cursor_--;
     pos_--;
   }
 
+  virtual bool SetBookmark();
+  virtual void ResetToBookmark();
+
  protected:
   virtual size_t SlowSeekForward(size_t delta) {
     // Fast case always handles seeking.
     return 0;
   }
   virtual bool ReadBlock() {
     // 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 v8::internal
 
 #endif  // V8_SCANNER_CHARACTER_STREAMS_H_