First pass at experimental omnibox API. There are plenty of rough edges and

chrome/browser/extensions/extension_message_service.cc

Index: chrome/browser/extensions/extension_message_service.cc
diff --git a/chrome/browser/extensions/extension_message_service.cc b/chrome/browser/extensions/extension_message_service.cc
index f3fb6a0a4088465c6bcc4979dfcf8643b902dd7f..2c7f693eb2f4d2e64b05582d7c12ace681624ea2 100644
--- a/chrome/browser/extensions/extension_message_service.cc
+++ b/chrome/browser/extensions/extension_message_service.cc
@@ -177,6 +177,12 @@ void ExtensionMessageService::RemoveEventListener(const std::string& event_name,
   }
 }
 
+bool ExtensionMessageService::HasEventListener(
+    const std::string& event_name) {
+  return (listeners_.find(event_name) != listeners_.end() &&
+          !listeners_[event_name].empty());
+}
+
 void ExtensionMessageService::AllocatePortIdPair(int* port1, int* port2) {
   AutoLock lock(next_port_id_lock_);