Handle load errors in deferred code

runtime/include/dart_api.h

Index: runtime/include/dart_api.h
===================================================================
--- runtime/include/dart_api.h	(revision 38794)
+++ runtime/include/dart_api.h	(working copy)
@@ -2624,6 +2624,21 @@
 /* TODO(turnidge): Consider returning Dart_Null() when the library is
  * not found to distinguish that from a true error case. */
 
+
+/**
+ * Report an loading error for the library.
+ *
+ * \param library The library that failed to load.
+ * \param error The Dart error instance containing the load error.
+ *
+ * \return If the VM handles the error, the return value is
+ * a null handle. If it doesn't handle the error, the error
+ * object is returned.
+ */
+DART_EXPORT Dart_Handle Dart_LibraryHandleError(Dart_Handle library,
+                                                Dart_Handle error);
+
+
 DART_EXPORT Dart_Handle Dart_LoadLibrary(Dart_Handle url,
                                          Dart_Handle source);