Allow SDKs to be analyzed that lack a definition of FutureOr<T>.

pkg/analyzer/lib/src/summary/summary_sdk.dart

Index: pkg/analyzer/lib/src/summary/summary_sdk.dart
diff --git a/pkg/analyzer/lib/src/summary/summary_sdk.dart b/pkg/analyzer/lib/src/summary/summary_sdk.dart
index b178fdcf081225890781a03e9d1281d0cfd2d21b..7e9e1f5efd577b0525458880b9b7df8d872711d7 100644
--- a/pkg/analyzer/lib/src/summary/summary_sdk.dart
+++ b/pkg/analyzer/lib/src/summary/summary_sdk.dart
@@ -15,6 +15,7 @@ import 'package:analyzer/src/generated/resolver.dart';
 import 'package:analyzer/src/generated/sdk.dart';
 import 'package:analyzer/src/generated/source.dart'
     show DartUriResolver, Source, SourceFactory;
+import 'package:analyzer/src/generated/testing/element_factory.dart';
 import 'package:analyzer/src/summary/idl.dart';
 import 'package:analyzer/src/summary/package_bundle_reader.dart';
 
@@ -192,7 +193,14 @@ class SummaryTypeProvider extends TypeProviderBase {
   @override
   InterfaceType get futureOrType {
     assert(_asyncLibrary != null);
-    _futureOrType ??= _getType(_asyncLibrary, "FutureOr");
+    try {
+      _futureOrType ??= _getType(_asyncLibrary, "FutureOr");
+    } on StateError {
+      // FutureOr<T> is still fairly new, so if we're analyzing an SDK that
+      // doesn't have it yet, create an element for it.
+      _futureOrType =
+          TypeProviderImpl.createPlaceholderFutureOr(futureType, objectType);
+    }
     return _futureOrType;
   }