[chrome-gnome-shell/feature/firefox] firefox-compat: check if callback is defined in sendMessage

[Yuri Konotopov <ykonotopov src gnome org>]

commit 3e74d31347c7ad2feb5cbb0d0580d5f555aaa13c
Author: Yuri Konotopov <ykonotopov gnome org>
Date:   Thu Dec 22 22:01:42 2016 +0400

    firefox-compat: check if callback is defined in sendMessage

 extension/include/compat-content-script.js |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/extension/include/compat-content-script.js b/extension/include/compat-content-script.js
index 96900b9..8bedd05 100644
--- a/extension/include/compat-content-script.js
+++ b/extension/include/compat-content-script.js
@@ -30,7 +30,10 @@ if(COMPAT.IS_FIREFOX)
 
                                        chrome.runtime.sendMessage(extensionId, message, options)
                                                .then(result => {
-                                                       responseCallback(cloneInto(result, window));
+                                                       if(typeof(responseCallback) == 'function')
+                                                       {
+                                                               responseCallback(cloneInto(result, window));
+                                                       }
                                                })
                                                .catch(err => {
                                                        console.error("firefox-external-messaging: 
runtime.sendMessage error", err);