Ignore deferred loading from dart backend.

sdk/lib/_internal/compiler/implementation/deferred_load.dart

Index: sdk/lib/_internal/compiler/implementation/deferred_load.dart
diff --git a/sdk/lib/_internal/compiler/implementation/deferred_load.dart b/sdk/lib/_internal/compiler/implementation/deferred_load.dart
index 310799ae3d1f471b3167c97cee66b8b923d920bc..0c0aa7b28dbbf217e2c51e069da34f64c49b8ad6 100644
--- a/sdk/lib/_internal/compiler/implementation/deferred_load.dart
+++ b/sdk/lib/_internal/compiler/implementation/deferred_load.dart
@@ -763,9 +763,10 @@ class DeferredLoadTask extends CompilerTask {
     }
     if (splitProgram && backend is DartBackend) {
       // TODO(sigurdm): Implement deferred loading for dart2dart.
-      compiler.reportFatalError(
+      compiler.reportWarning(
           lastDeferred,
           MessageKind.DEFERRED_LIBRARY_DART_2_DART);
+      splitProgram = false;
     }
   }