Improve SeqString::Truncate for latest allocated strings.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 933a07599a455f6a19774a84b198b41e3aefdd13..52ae083ae1b02b0dbdaf2bc1df66c363816cd319 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -7754,8 +7754,8 @@ class SeqString: public String {
   // Truncate the string in-place if possible and return the result.
   // In case of new_length == 0, the empty string is returned without
   // truncating the original string.
-  MUST_USE_RESULT String* Truncate(int new_length);
-
+  MUST_USE_RESULT static Handle<String> Truncate(Handle<SeqString> string,
+                                                 int new_length);
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(SeqString);
 };