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

src/regexp-macro-assembler-irregexp.cc

Index: src/regexp-macro-assembler-irregexp.cc
===================================================================
--- src/regexp-macro-assembler-irregexp.cc	(revision 865)
+++ src/regexp-macro-assembler-irregexp.cc	(working copy)
@@ -226,6 +226,12 @@
 }
 
 
+void RegExpMacroAssemblerIrregexp::CheckNotAtStart(Label* on_not_at_start) {
+  Emit(BC_CHECK_NOT_AT_START);
+  EmitOrLink(on_not_at_start);
+}
+
+
 void RegExpMacroAssemblerIrregexp::CheckNotCharacter(uc16 c,
                                                      Label* on_not_equal) {
   Emit(BC_CHECK_NOT_CHAR);