Recommit introducing short external strings.

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index cfd96256e1be89c3da505da7624c7007692e4402..9f4f505e1d9d04a6695b1cd2d92a776e982263d0 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -110,6 +110,16 @@ inline Heap* _inline_get_heap_();
   V(Map, external_string_map, ExternalStringMap)                               \
   V(Map, external_string_with_ascii_data_map, ExternalStringWithAsciiDataMap)  \
   V(Map, external_ascii_string_map, ExternalAsciiStringMap)                    \
+  V(Map, short_external_symbol_map, ShortExternalSymbolMap)                    \
+  V(Map,                                                                       \
+    short_external_symbol_with_ascii_data_map,                                 \
+    ShortExternalSymbolWithAsciiDataMap)                                       \
+  V(Map, short_external_ascii_symbol_map, ShortExternalAsciiSymbolMap)         \
+  V(Map, short_external_string_map, ShortExternalStringMap)                    \
+  V(Map,                                                                       \
+    short_external_string_with_ascii_data_map,                                 \
+    ShortExternalStringWithAsciiDataMap)                                       \
+  V(Map, short_external_ascii_string_map, ShortExternalAsciiStringMap)         \
   V(Map, undetectable_string_map, UndetectableStringMap)                       \
   V(Map, undetectable_ascii_string_map, UndetectableAsciiStringMap)            \
   V(Map, external_pixel_array_map, ExternalPixelArrayMap)                      \