Support StringCharCodeAt in hydrogen/lithium.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index c136dc59b543de6ac30497d8f4a2776085cf47bd..d8832020f1bfff885044f5d3e2b84fcd1b83d79f 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -455,6 +455,7 @@ const uint32_t kShortcutTypeTag = kConsStringTag;
 
 enum InstanceType {
   // String types.
+  // FIRST_STRING_TYPE
   SYMBOL_TYPE = kTwoByteStringTag | kSymbolTag | kSeqStringTag,
   ASCII_SYMBOL_TYPE = kAsciiStringTag | kSymbolTag | kSeqStringTag,
   CONS_SYMBOL_TYPE = kTwoByteStringTag | kSymbolTag | kConsStringTag,
@@ -471,6 +472,7 @@ enum InstanceType {
   EXTERNAL_STRING_TYPE = kTwoByteStringTag | kExternalStringTag,
   EXTERNAL_STRING_WITH_ASCII_DATA_TYPE =
       kTwoByteStringTag | kExternalStringTag | kAsciiDataHintTag,
+  // LAST_STRING_TYPE
   EXTERNAL_ASCII_STRING_TYPE = kAsciiStringTag | kExternalStringTag,
   PRIVATE_EXTERNAL_ASCII_STRING_TYPE = EXTERNAL_ASCII_STRING_TYPE,
 
@@ -532,6 +534,8 @@ enum InstanceType {
   LAST_TYPE = JS_FUNCTION_TYPE,
   INVALID_TYPE = FIRST_TYPE - 1,
   FIRST_NONSTRING_TYPE = MAP_TYPE,
+  FIRST_STRING_TYPE = FIRST_TYPE,
+  LAST_STRING_TYPE = FIRST_NONSTRING_TYPE - 1,
   // Boundaries for testing for an external array.
   FIRST_EXTERNAL_ARRAY_TYPE = EXTERNAL_BYTE_ARRAY_TYPE,
   LAST_EXTERNAL_ARRAY_TYPE = EXTERNAL_FLOAT_ARRAY_TYPE,