Remember when an isolate was paused and subtly display it in Obseravatory

runtime/vm/isolate.h

Index: runtime/vm/isolate.h
diff --git a/runtime/vm/isolate.h b/runtime/vm/isolate.h
index 3a42366f3dba9df165d9fff1d6a917e96e72cb45..cc07c1bb2f3de4620214165f8533b09ab1d9b1f4 100644
--- a/runtime/vm/isolate.h
+++ b/runtime/vm/isolate.h
@@ -447,6 +447,11 @@ class Isolate : public BaseIsolate {
   // Requests that the debugger resume execution.
   void Resume() {
     resume_request_ = true;
+    last_resume_timestamp_ = OS::GetCurrentTimeMillis();
+  }
+
+  int64_t last_resume_timestamp() const {
+    return last_resume_timestamp_;
   }
 
   // Returns whether the vm service has requested that the debugger
@@ -803,6 +808,7 @@ class Isolate : public BaseIsolate {
   Debugger* debugger_;
   bool single_step_;
   bool resume_request_;
+  int64_t last_resume_timestamp_;
   bool has_compiled_;
   Flags flags_;
   Random random_;