Abort tracing in type inference in the presence of await.

pkg/compiler/lib/src/inferrer/concrete_types_inferrer.dart

Index: pkg/compiler/lib/src/inferrer/concrete_types_inferrer.dart
diff --git a/pkg/compiler/lib/src/inferrer/concrete_types_inferrer.dart b/pkg/compiler/lib/src/inferrer/concrete_types_inferrer.dart
index 4f952146517052a087a3c66a7363b3057c792484..46cd38607d3652f32995bf7207a88298c8a43236 100644
--- a/pkg/compiler/lib/src/inferrer/concrete_types_inferrer.dart
+++ b/pkg/compiler/lib/src/inferrer/concrete_types_inferrer.dart
@@ -2243,6 +2243,11 @@ class ConcreteTypesInferrer
     return result;
   }
 
+  ConcreteType registerAwait(Node node, ConcreteType argumentType) {
+    // TODO(polux): Properly handle await expressions.
+    return types.dynamicType;
+  }
+
   @override
   void setDefaultTypeOfParameter(ParameterElement parameter,
                                  ConcreteType type) {