Initial implementation of the useragent switcher

Change-Id: Iaa8262a678902645dbfaa8a53fe7212af7d9d53c
diff --git a/src/com/android/browser/PreferenceKeys.java b/src/com/android/browser/PreferenceKeys.java
index f7230df..cff9f70 100644
--- a/src/com/android/browser/PreferenceKeys.java
+++ b/src/com/android/browser/PreferenceKeys.java
@@ -78,6 +78,7 @@
     static final String PREF_USE_MOST_VISITED_HOMEPAGE = "use_most_visited_homepage";
     static final String PREF_USE_INSTANT_SEARCH = "use_instant_search";
     static final String PREF_FULLSCREEN = "fullscreen";
+    static final String PREF_ENABLE_USERAGENT_SWITCHER = "enable_useragent_switcher";
 
     // ----------------------
     // Keys for privacy_security_preferences.xml