[linux] add InitWidget() to run in external message loop

platform/darwin/tray.m

@@ -82,6 +82,9 @@ void native_loop() {
     [NSApp run];
 }
 
+void external_main_loop() {
+}
+
 void exit_loop() {
     // Clear all notifications.
     [[NSUserNotificationCenter defaultUserNotificationCenter] removeAllDeliveredNotifications];

platform/linux/tray.c

@@ -148,7 +148,7 @@ void init(const char* title, struct image imageData)
 
 void native_loop()
 {
-  gtk_widget_show_all(menu);
+  external_main_loop();
   gtk_main ();
 }
 
@@ -157,5 +157,9 @@ void exit_loop()
   gtk_main_quit();
 }
 
+void external_main_loop() {
+  gtk_widget_show_all(menu);
+}
+
 
 #endif // NATIVE_C

platform/windows/tray.c

@@ -43,6 +43,10 @@ void clear_menu_items()
     }
 }
 
+void external_main_loop ()
+{
+}
+
 void native_loop()
 {
     MSG msg;

trayhost.go

@@ -66,6 +66,11 @@ func Exit() {
 	C.exit_loop()
 }
 
+// init widget for running in other gtk_main loop
+func InitWidget() {
+	C.external_main_loop()
+}
+
 // SeparatorMenuItem creates a separator MenuItem.
 func SeparatorMenuItem() MenuItem { return MenuItem{Title: ""} }