Bug 1276910 - Do not show "Add to home screen" prompt in private browsing. r=margaret

MozReview-Commit-ID: DFoMnyx4Gde

--HG--
extra : rebase_source : 4f91aea87e161fa08d07677f5c90717e7514e59c
extra : histedit_source : b8f02f27216478603d61c3f71562da74e0297e16

mobile/android/base/java/org/mozilla/gecko/promotion/AddToHomeScreenPromotion.java

@@ -134,6 +134,11 @@ public class AddToHomeScreenPromotion extends BrowserAppDelegate implements Tabs
             return;
         }
 
+        if (tab.isPrivate()) {
+            // Never show the prompt for private browsing tabs.
+            return;
+        }
+
         if (!isInForeground) {
             // We only want to show this prompt if this tab is in the foreground and not on top
             // of the tabs tray.