Adds a special case for sending an int over a port with the native API.

runtime/vm/message.cc

Index: runtime/vm/message.cc
diff --git a/runtime/vm/message.cc b/runtime/vm/message.cc
index 54f40b4eeb77c91cee4a35bbd2c5d356a0e75b48..f9a341909fef1fc87acc837f7ee9a4cb8305eefd 100644
--- a/runtime/vm/message.cc
+++ b/runtime/vm/message.cc
@@ -194,7 +194,12 @@ void MessageQueue::PrintJSON(JSONStream* stream) {
     message.AddPropertyF("name", "Isolate Message (%" Px ")", current->Id());
     message.AddPropertyF("messageObjectId", "messages/%" Px "",
                          current->Id());
-    message.AddProperty("size", current->len());
+    if (current->type() == Message::kDataType) {
+      message.AddProperty("size", current->len());
+    } else {
+      ASSERT(current->type() == Message::kIntegerType);
+      message.AddProperty("integer", current->integer());
+    }
     message.AddProperty("index", depth++);
     message.AddPropertyF("_destinationPort", "%" Pd64 "",
         static_cast<int64_t>(current->dest_port()));