Bug 1274052 - Log search engine identifier as extra. r=grisha

For privacy, custom search engines are "other".

MozReview-Commit-ID: GTM7d9k8JFZ

--HG--
extra : rebase_source : c7a1f8ba5694bb05680ea768110eb346dae91be0

mobile/android/base/java/org/mozilla/gecko/BrowserApp.java

@@ -3896,7 +3896,11 @@ public class BrowserApp extends GeckoApp
         if (!Tabs.getInstance().getSelectedTab().isPrivate()) {
             storeSearchQuery(text);
         }
-        recordSearch(GeckoSharedPrefs.forProfile(this), engine.getEngineIdentifier(), method);
+
+        // We don't use SearchEngine.getEngineIdentifier because it can
+        // return a custom search engine name, which is a privacy concern.
+        final String identifierToRecord = (engine.identifier != null) ? engine.identifier : "other";
+        recordSearch(GeckoSharedPrefs.forProfile(this), identifierToRecord, method);
         openUrlAndStopEditing(text, engine.name);
     }