Bug 975423 - Don't show sync promo banner ever again after user hits close button. r=bnicholson

mobile/android/components/Snippets.js

@@ -340,11 +340,16 @@ function loadSyncPromoBanner() {
       let text = stringBundle.GetStringFromName("promoBanner.message.text");
       let link = stringBundle.GetStringFromName("promoBanner.message.link");
 
-      Home.banner.add({
+      let id = Home.banner.add({
         text: text + "<a href=\"#\">" + link + "</a>",
         icon: "drawable://sync_promo",
         onclick: function() {
           Accounts.launchSetup();
+        },
+        ondismiss: function() {
+          // Remove the sync promo message from the banner and never try to show it again.
+          Home.banner.remove(id);
+          Services.prefs.setBoolPref("browser.snippets.syncPromo.enabled", false);
         }
       });
     },