Add some support for the code-point code-unit distinction.

runtime/lib/regexp_jsc.cc

Index: runtime/lib/regexp_jsc.cc
diff --git a/runtime/lib/regexp_jsc.cc b/runtime/lib/regexp_jsc.cc
index 31cee70a1f59e91044cb4d09853dbaa8e4b0a870..a81f2134868f5dfd9e1d3adce8e397a08350f88e 100644
--- a/runtime/lib/regexp_jsc.cc
+++ b/runtime/lib/regexp_jsc.cc
@@ -19,7 +19,7 @@ static uint16_t* GetTwoByteData(const String& str) {
   Zone* zone = Isolate::Current()->current_zone();
   uint16_t* two_byte_str = zone->Alloc<uint16_t>(str.Length());
   for (intptr_t i = 0; i < str.Length(); i++) {
-    two_byte_str[i] = str.CharAt(i);
+    two_byte_str[i] = str.CodeUnitAt(i);
   }
   return two_byte_str;
 }