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

runtime/vm/intermediate_language.cc

Index: runtime/vm/intermediate_language.cc
diff --git a/runtime/vm/intermediate_language.cc b/runtime/vm/intermediate_language.cc
index 21d220d34bbd9eebe1fbbfadde59632187145523..78c8a099480024dca67f2023034d1e75ffe78c25 100644
--- a/runtime/vm/intermediate_language.cc
+++ b/runtime/vm/intermediate_language.cc
@@ -219,7 +219,7 @@ static bool CompareNames(const Library& lib,
                          const char* test_name,
                          const String& name) {
   // If both names are private mangle test_name before comparison.
-  if ((name.CharAt(0) == '_') && (test_name[0] == '_')) {
+  if ((name.CodeUnitAt(0) == '_') && (test_name[0] == '_')) {
     const String& test_name_symbol = String::Handle(Symbols::New(test_name));
     return String::Handle(lib.PrivateName(test_name_symbol)).Equals(name);
   }