Fix bug in Utf8::CodePointCount which was causing some strings with latin1

vm/symbols.cc

Index: vm/symbols.cc
===================================================================
--- vm/symbols.cc	(revision 15591)
+++ vm/symbols.cc	(working copy)
@@ -102,7 +102,7 @@
   Utf8::Type type;
   intptr_t str_len = strlen(str);
   const uint8_t* utf8_array = reinterpret_cast<const uint8_t*>(str);
-  intptr_t len = Utf8::CodePointCount(utf8_array, str_len, &type);
+  intptr_t len = Utf8::CodeUnitCount(utf8_array, str_len, &type);
   Zone* zone = Isolate::Current()->current_zone();
   if (len == 0) {
     return Symbols::New(reinterpret_cast<uint8_t*>(NULL), 0);