Remember when a variable has been expanded/unexpanded in the debugger.

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

Index: runtime/observatory/lib/src/elements/debugger.dart
diff --git a/runtime/observatory/lib/src/elements/debugger.dart b/runtime/observatory/lib/src/elements/debugger.dart
index 383e257a6d7b2425ac65216d237d7d1dc0282f70..ae0ab6f24b11cfa5ff6361146561e87ac4b37a39 100644
--- a/runtime/observatory/lib/src/elements/debugger.dart
+++ b/runtime/observatory/lib/src/elements/debugger.dart
@@ -1717,6 +1717,11 @@ class DebuggerFrameElement extends ObservatoryElement {
 
   DebuggerFrameElement.created() : super.created();
 
+
+  String makeExpandKey(String key) {
+    return '${frame.function.qualifiedName}/${key}';
+  }
+
   bool matchFrame(Frame newFrame) {
     return newFrame.function.id == frame.function.id;
   }