Implement 'print', 'up', 'down', and 'frame' commands in the Observatory debugger.

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 71c6a09682c5139f00514899c99a8d431b6a6e8e..9ec50054f776f19234d30c4341c520db1b6fd6ca 100644
--- a/runtime/observatory/lib/src/service/object.dart
+++ b/runtime/observatory/lib/src/service/object.dart
@@ -1207,6 +1207,15 @@ class Isolate extends ServiceObjectOwner with Coverage {
     return invokeRpc('eval', params);
   }
 
+  Future<ServiceObject> evalFrame(int framePos,
+                                  String expression) {
+    Map params = {
+      'frame': framePos,
+      'expression': expression,
+    };
+    return invokeRpc('evalFrame', params);
+  }
+
   Future<ServiceObject> getRetainedSize(ServiceObject target) {
     Map params = {
       'targetId': target.id,