improve static type analysis for `await for`

pkg/analyzer/lib/src/task/strong/rules.dart

Index: pkg/analyzer/lib/src/task/strong/rules.dart
diff --git a/pkg/analyzer/lib/src/task/strong/rules.dart b/pkg/analyzer/lib/src/task/strong/rules.dart
index 3cd6db2a6875935017079a8d1dbf7c4445e32f4d..32236a8aaee630c3d0584190def357676a92d62e 100644
--- a/pkg/analyzer/lib/src/task/strong/rules.dart
+++ b/pkg/analyzer/lib/src/task/strong/rules.dart
@@ -57,10 +57,7 @@ class TypeRules {
   /// return null.
   FunctionType getCallMethodType(DartType t) {
     if (t is InterfaceType) {
-      ClassElement element = t.element;
-      InheritanceManager manager = new InheritanceManager(element.library);
-      FunctionType callType = manager.lookupMemberType(t, "call");
-      return callType;
+      return t.lookUpMethod("call", null)?.type;
     }
     return null;
   }