Add an operation that checks whether we are at the start of the string.

src/regexp-macro-assembler.h

 // Copyright 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 57 matching lines @@
   virtual void CheckCharacters(
       Vector<const uc16> str,
       int cp_offset,
       Label* on_failure) = 0;
   // Check the current input position against a register.  If the register is
   // equal to the current position then go to the label.  If the label is NULL
   // then backtrack instead.
   virtual void CheckCurrentPosition(
       int register_index,
       Label* on_equal) = 0;
+  virtual void CheckNotAtStart(Label* on_not_at_start) = 0;
   virtual void CheckNotBackReference(int start_reg, Label* on_no_match) = 0;
   virtual void CheckNotBackReferenceIgnoreCase(int start_reg,
                                                Label* on_no_match) = 0;
   // Check the current character for a match with a literal character.  If we
   // fail to match then goto the on_failure label.  End of input always
   // matches.  If the label is NULL then we should pop a backtrack address off
   // the stack and go to that.
   virtual void CheckNotCharacter(uc16 c, Label* on_not_equal) = 0;
   // Bitwise or the current character with the given constant and then
   // check for a match with c.
@@ skipping 88 matching lines @@
   ArraySlice GetBuffer(Vector<T> values);
  private:
   size_t byte_array_size_;
   Handle<ByteArray> current_byte_array_;
   int current_byte_array_free_offset_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_REGEXP_MACRO_ASSEMBLER_H_