Fix shutdown race when running Dart on the message loop

tonic/dart_message_handler.h

Index: tonic/dart_message_handler.h
diff --git a/tonic/dart_message_handler.h b/tonic/dart_message_handler.h
index 5cb2f9aad94c2be758c8a09a46ba659794a5b16f..a6ab3d3122070bc6a9775411665d5ba852ddf463 100644
--- a/tonic/dart_message_handler.h
+++ b/tonic/dart_message_handler.h
@@ -20,6 +20,27 @@ class DartMessageHandler {
   // Messages for the current isolate will be scheduled on |runner|.
   void Initialize(const scoped_refptr<base::SingleThreadTaskRunner>& runner);
 
+  // Request the message loop to quit when isolate exits? Default is true.
+  void set_quit_message_loop_when_isolate_exits(
+      bool quit_message_loop_when_isolate_exits) {
+    quit_message_loop_when_isolate_exits_ =
+        quit_message_loop_when_isolate_exits;
+  }
+
+  bool quit_message_loop_when_isolate_exits() const {
+    return quit_message_loop_when_isolate_exits_;
+  }
+
+  // Did the isolate exit?
+  bool isolate_exited() const {
+    return isolate_exited_;
+  }
+
+  // Did the isolate have an uncaught exception error?
+  bool isolate_had_uncaught_exception_error() const {
+    return isolate_had_uncaught_exception_error_;
+  }
+
  protected:
   // Called from an unknown thread for each message.
   void OnMessage(DartState* dart_state);
@@ -39,6 +60,9 @@ class DartMessageHandler {
   }
 
   bool handled_first_message_;
+  bool quit_message_loop_when_isolate_exits_;
+  bool isolate_exited_;
+  bool isolate_had_uncaught_exception_error_;
   scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
 
  private: