Tentative implementation of string slices (hidden under the flag --string-slices).

src/regexp-macro-assembler.cc

Index: src/regexp-macro-assembler.cc
diff --git a/src/regexp-macro-assembler.cc b/src/regexp-macro-assembler.cc
index 55782431bec353820f868b71b94b4d4cb0a661e6..a48cb0c54681eee6be6ed188c1fef51bc3586680 100644
--- a/src/regexp-macro-assembler.cc
+++ b/src/regexp-macro-assembler.cc
@@ -74,6 +74,12 @@ bool NativeRegExpMacroAssembler::CanReadUnaligned() {
 const byte* NativeRegExpMacroAssembler::StringCharacterPosition(
     String* subject,
     int start_index) {
+  // Unpack sliced string.
+  if (subject->IsSlicedString()) {
+     SlicedString* slice = SlicedString::cast(subject);
+     subject = slice->parent();
+     start_index += slice->offset();
+  }
   // Not just flat, but ultra flat.
   ASSERT(subject->IsExternalString() || subject->IsSeqString());
   ASSERT(start_index >= 0);
@@ -130,7 +136,9 @@ NativeRegExpMacroAssembler::Result NativeRegExpMacroAssembler::Match(
   }
   // Ensure that an underlying string has the same ascii-ness.
   bool is_ascii = subject_ptr->IsAsciiRepresentation();
-  ASSERT(subject_ptr->IsExternalString() || subject_ptr->IsSeqString());
+  ASSERT(subject_ptr->IsExternalString() ||
+         subject_ptr->IsSeqString() ||
+         subject_ptr->IsSlicedString());
   // String is now either Sequential or External
   int char_size_shift = is_ascii ? 0 : 1;
   int char_length = end_offset - start_offset;