Fix for issue 21398 (only send "literal like" objects across isolates spawned using spawnURI

runtime/vm/isolate.h

Index: runtime/vm/isolate.h
===================================================================
--- runtime/vm/isolate.h	(revision 42788)
+++ runtime/vm/isolate.h	(working copy)
@@ -170,6 +170,12 @@
     ASSERT(main_port_ == 0);  // Only set main port once.
     main_port_ = port;
   }
+  Dart_Port origin_id() const { return origin_id_; }
+  void set_origin_id(Dart_Port id) {
+    ASSERT((id == main_port_ && origin_id_ == 0) ||
+           (origin_id_ == main_port_));
+    origin_id_ = id;
+  }
   void set_pause_capability(uint64_t value) { pause_capability_ = value; }
   uint64_t pause_capability() const { return pause_capability_; }
   void set_terminate_capability(uint64_t value) {
@@ -633,6 +639,7 @@
   char* name_;
   int64_t start_time_;
   Dart_Port main_port_;
+  Dart_Port origin_id_;  // Isolates created by spawnFunc have some origin id.
   uint64_t pause_capability_;
   uint64_t terminate_capability_;
   Heap* heap_;