Add BusConnection::gconnection() function.

src/common/chromeos/dbus/dbus.h

Index: src/common/chromeos/dbus/dbus.h
diff --git a/src/common/chromeos/dbus/dbus.h b/src/common/chromeos/dbus/dbus.h
index f11a7ef4547f93801b9b7a9af74c1d2f5c95188e..81840c53bc114092e345befa3e339a2b10d78983 100644
--- a/src/common/chromeos/dbus/dbus.h
+++ b/src/common/chromeos/dbus/dbus.h
@@ -46,6 +46,11 @@ class BusConnection {
     return *this;
   }
 
+  const value_type& g_connection() const {
+    DCHECK(object_) << "referencing an empty connection";
+    return object_;
+  }
+
  private:
   friend void swap(BusConnection& x, BusConnection& y);