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

runtime/vm/message_handler.h

Index: runtime/vm/message_handler.h
diff --git a/runtime/vm/message_handler.h b/runtime/vm/message_handler.h
index 07fa5ab09b7a80c9240434f0b1f30a7cc11617c8..78c5f6c7e5ec4173641a9f06b21b32b9fb365752 100644
--- a/runtime/vm/message_handler.h
+++ b/runtime/vm/message_handler.h
@@ -96,6 +96,11 @@ class MessageHandler {
     return paused_on_exit_;
   }
 
+  // Timestamp of the paused on start or paused on exit.
+  int64_t paused_timestamp() const {
+    return paused_timestamp_;
+  }
+
   class AcquiredQueues : public ValueObject {
    public:
     AcquiredQueues();
@@ -207,6 +212,7 @@ class MessageHandler {
   bool pause_on_exit_;
   bool paused_on_start_;
   bool paused_on_exit_;
+  int64_t paused_timestamp_;
   ThreadPool* pool_;
   ThreadPool::Task* task_;
   StartCallback start_callback_;