Start using String type info:

src/type-info.h

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 138 matching lines @@
   inline bool IsInteger32() {
     ASSERT(type_ != kUninitializedType);
     return ((type_ & kInteger32Type) == kInteger32Type);
   }
 
   inline bool IsDouble() {
     ASSERT(type_ != kUninitializedType);
     return ((type_ & kDoubleType) == kDoubleType);
   }
 
+  inline bool IsString() {
+    ASSERT(type_ != kUninitializedType);
+    return ((type_ & kStringType) == kStringType);
+  }
+
   inline bool IsUninitialized() {
     return type_ == kUninitializedType;
   }
 
   const char* ToString() {
     switch (type_) {
       case kUnknownType: return "UnknownType";
       case kPrimitiveType: return "PrimitiveType";
       case kNumberType: return "NumberType";
       case kInteger32Type: return "Integer32Type";
@@ skipping 61 matching lines @@
 }
 
 
 TypeInfo TypeInfo::Uninitialized() {
   return TypeInfo(kUninitializedType);
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_TYPE_INFO_H_