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

runtime/vm/port.cc

Index: runtime/vm/port.cc
===================================================================
--- runtime/vm/port.cc	(revision 29317)
+++ runtime/vm/port.cc	(working copy)
@@ -82,6 +82,12 @@
   ASSERT(index >= 0);
   map_[index].live = true;
   map_[index].handler->increment_live_ports();
+  if (FLAG_trace_isolates) {

[Ivan Posva, 2013/10/27 14:33:17]

Added tracing support.

+    OS::Print("[^] Live port: \n"
+              "\thandler:    %s\n"
+              "\tport:       %" Pd64 "\n",
+              map_[index].handler->name(), port);
+  }
 }
 
 
@@ -137,6 +143,13 @@
   used_++;
   MaintainInvariants();
 
+  if (FLAG_trace_isolates) {

[Ivan Posva, 2013/10/27 14:33:17]

ditto

+    OS::Print("[+] Opening port: \n"
+              "\thandler:    %s\n"
+              "\tport:       %" Pd64 "\n",
+              handler->name(), entry.port);
+  }
+
   return entry.port;
 }