Make Dart_LoadLibrary and Dart_LoadSource take line and column offsets like Dart_LoadScript.

runtime/vm/unit_test.cc

Index: runtime/vm/unit_test.cc
diff --git a/runtime/vm/unit_test.cc b/runtime/vm/unit_test.cc
index 5c0a2c86d01da945233b81209bfc26b79c5be858..3595d4fb872b0c24a406cf31a9dc1ad040833e6d 100644
--- a/runtime/vm/unit_test.cc
+++ b/runtime/vm/unit_test.cc
@@ -104,7 +104,8 @@ static Dart_Handle LibraryTagHandler(Dart_LibraryTag tag,
     return Dart_LoadSource(library,
                            url,
                            Builtin::PartSource(Builtin::kIOLibrary,
-                                               url_chars));
+                                               url_chars),
+                           0, 0);
   }
   return DartUtils::LoadSource(library, url, tag, url_chars);
 }