Split dart:builtin into dart:builtin and dart:io.

runtime/bin/dartutils.h

Index: runtime/bin/dartutils.h
diff --git a/runtime/bin/dartutils.h b/runtime/bin/dartutils.h
index f18d2c6c546aa3de36a5b540b9659e54c1043574..9b04bfe14e7852b2e18fdb637c1ea8af0b40c216 100644
--- a/runtime/bin/dartutils.h
+++ b/runtime/bin/dartutils.h
@@ -68,6 +68,7 @@ class DartUtils {
                                      const char* name,
                                      const char* val);
   static bool IsDartSchemeURL(const char* url_name);
+  static bool IsDartIOLibURL(const char* url_name);
   static Dart_Handle CanonicalizeURL(CommandLineOptions* url_mapping,
                                      Dart_Handle library,
                                      const char* url_str);
@@ -82,7 +83,7 @@ class DartUtils {
   static const char* kBuiltinLibURL;
   static const char* kCoreLibURL;
   static const char* kCoreImplLibURL;
-  static const char* kCoreNativeWrappersLibURL;
+  static const char* kIOLibURL;
 
   static const char* kIdFieldName;