Async-step, first cut.

runtime/observatory/lib/src/service/object.dart

Index: runtime/observatory/lib/src/service/object.dart
diff --git a/runtime/observatory/lib/src/service/object.dart b/runtime/observatory/lib/src/service/object.dart
index c17db626d72d35f26b2ac664c6aa88403b6b487a..fa73cf6266a6b429e6185147b7eab837fa8af9ef 100644
--- a/runtime/observatory/lib/src/service/object.dart
+++ b/runtime/observatory/lib/src/service/object.dart
@@ -1622,6 +1622,7 @@ class ServiceEvent extends ServiceObject {
   @observable Breakpoint breakpoint;
   @observable Frame topFrame;
   @observable Instance exception;
+  @observable Instance asyncContinuation;
   @observable ServiceObject inspectee;
   @observable ByteData data;
   @observable int count;
@@ -1661,6 +1662,9 @@ class ServiceEvent extends ServiceObject {
     if (map['exception'] != null) {
       exception = map['exception'];
     }
+    if (map['_asyncContinuation'] != null) {
+      asyncContinuation = map['_asyncContinuation'];
+    }
     if (map['inspectee'] != null) {
       inspectee = map['inspectee'];
     }