Reland https://code.google.com/p/dart/source/detail?r=29315:

runtime/vm/isolate.cc

Index: runtime/vm/isolate.cc
===================================================================
--- runtime/vm/isolate.cc	(revision 29317)
+++ runtime/vm/isolate.cc	(working copy)
@@ -534,6 +534,10 @@
     args.SetAt(0, Instance::Handle(func.ImplicitStaticClosure()));
     args.SetAt(1, is_spawn_uri ? Bool::True() : Bool::False());
 
+    // Dispatching through _startIsolate will open a control port as a live
+    // port. Account for this by increasing the number of open control ports.
+    isolate->message_handler()->increment_control_ports();
+
     const Library& lib = Library::Handle(Library::IsolateLibrary());
     const String& entry_name = String::Handle(String::New("_startIsolate"));
     const Function& entry_point =