Add freeze tab menu option

  Adds a freeze tab menu option hidden behind about:debug for now.

Change-Id: I1b321de6a5dbcb13e87f6e658439f727970b0e4f
diff --git a/res/menu/browser.xml b/res/menu/browser.xml
index 90357e9..6eadcba 100644
--- a/res/menu/browser.xml
+++ b/res/menu/browser.xml
@@ -65,6 +65,9 @@
             android:id="@+id/save_webarchive_menu_id"
             android:title="@string/menu_save_webarchive" />
         <item
+            android:id="@+id/freeze_tab_menu_id"
+            android:title="@string/menu_freeze_tab" />
+        <item
             android:id="@+id/page_info_menu_id"
             android:title="@string/page_info"
             android:icon="@drawable/ic_pageinfo_holo_dark"