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

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index 6cd4f840b93e4abfcd052e2ab71392dda182b2b1..b8c8b4994a304325d35fc1f33fc751e1416a3f2b 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -87,6 +87,8 @@ inline Heap* _inline_get_heap_();
   V(Map, symbol_map, SymbolMap)                                                \
   V(Map, cons_string_map, ConsStringMap)                                       \
   V(Map, cons_ascii_string_map, ConsAsciiStringMap)                            \
+  V(Map, sliced_string_map, SlicedStringMap)                                   \
+  V(Map, sliced_ascii_string_map, SlicedAsciiStringMap)                        \
   V(Map, ascii_symbol_map, AsciiSymbolMap)                                     \
   V(Map, cons_symbol_map, ConsSymbolMap)                                       \
   V(Map, cons_ascii_symbol_map, ConsAsciiSymbolMap)                            \