Introduce (private) ZLibFilter to dart:io.

runtime/bin/dartutils.cc

Index: runtime/bin/dartutils.cc
diff --git a/runtime/bin/dartutils.cc b/runtime/bin/dartutils.cc
index 3e40dede01210da3967bd79913c3e1a24ae54969..06e478b30cf9677c95e061de5a46b9bf3be5da06 100644
--- a/runtime/bin/dartutils.cc
+++ b/runtime/bin/dartutils.cc
@@ -509,6 +509,23 @@ Dart_Handle DartUtils::NewDartOSError(OSError* os_error) {
 }
 
 
+Dart_Handle DartUtils::NewInternalError(const char* message) {
+  Dart_Handle url = Dart_NewString("dart:io");
+  if (Dart_IsError(url)) return url;
+  Dart_Handle lib = Dart_LookupLibrary(url);
+  if (Dart_IsError(lib)) return lib;
+  Dart_Handle class_name = Dart_NewString("InternalError");
+  if (Dart_IsError(class_name)) return class_name;
+  Dart_Handle clazz = Dart_GetClass(lib, class_name);
+  if (Dart_IsError(clazz)) return clazz;
+  Dart_Handle args[1];
+  args[0] = Dart_NewString(message);
+  if (Dart_IsError(args[0])) return args[0];
+  Dart_Handle err = Dart_New(clazz, Dart_Null(), 1, args);
+  return err;
+}
+
+
 void DartUtils::SetOriginalWorkingDirectory() {
   original_working_directory = Directory::Current();
 }