Allow users to see more elements of a list/map in Observatory.

runtime/observatory/lib/src/elements/instance_ref.dart

Index: runtime/observatory/lib/src/elements/instance_ref.dart
diff --git a/runtime/observatory/lib/src/elements/instance_ref.dart b/runtime/observatory/lib/src/elements/instance_ref.dart
index 86727ae8d36b07448cf08caa438fe8b4bec83b47..cbf5eae1e83c03c7bed1108b34a91eda07aa208b 100644
--- a/runtime/observatory/lib/src/elements/instance_ref.dart
+++ b/runtime/observatory/lib/src/elements/instance_ref.dart
@@ -4,6 +4,7 @@
 
 library instance_ref_element;
 
+import 'dart:async';
 import 'package:polymer/polymer.dart';
 import 'package:observatory/service.dart';
 import 'service_ref.dart';
@@ -58,4 +59,15 @@ class InstanceRefElement extends ServiceRefElement {
   String makeExpandKey(String key) {
     return '${expandKey}/${key}';
   }
+
+  Future showMore() async {
+    Instance instance = ref;
+    if (instance.isList) {
+      await instance.reload(count: instance.elements.length * 2);
+    } else if (instance.isMap) {
+      await instance.reload(count: instance.associations.length * 2);
+    } else if (instance.isTypedData) {
+      await instance.reload(count: instance.typedElements.length * 2);
+    }
+  }
 }