Change Dart_GetNativeBooleanArgument to use class Ids and direct

runtime/vm/dart_api_impl.h

Index: runtime/vm/dart_api_impl.h
===================================================================
--- runtime/vm/dart_api_impl.h	(revision 31244)
+++ runtime/vm/dart_api_impl.h	(working copy)
@@ -209,6 +209,11 @@
                                   int arg_index,
                                   void** peer);
 
+  // Helper function to get the boolean value of a Bool native argument.
+  static bool GetNativeBooleanArgument(Dart_NativeArguments args,
+                                       int arg_index,
+                                       bool* value);
+
   // Helper function to set the return value of native functions.
   static void SetReturnValue(NativeArguments* args, Dart_Handle retval) {
     args->SetReturnUnsafe(UnwrapHandle(retval));