Fix incognito menu item in overflow menu

This patch allows the incognito NTP menu item to be shown on incognito
pages.

Bug=812544

Change-Id: I99f002915979e98814ab9900ad9c3d202f70480f
Reviewed-on: https://chromium-review.googlesource.com/922241Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537072}

chrome/android/java/src/org/chromium/chrome/browser/appmenu/AppMenuPropertiesDelegate.java

@@ -253,7 +253,7 @@ public class AppMenuPropertiesDelegate {
         // findItem(...).setEnabled(...)" is not enough here, because of the inflated
         // main_menu.xml contains multiple items with the same id in different groups
         // e.g.: new_incognito_tab_menu_id.
-        disableEnableMenuItem(menu, R.id.new_incognito_tab_menu_id, !isIncognito,
+        disableEnableMenuItem(menu, R.id.new_incognito_tab_menu_id, true,
                 PrefServiceBridge.getInstance().isIncognitoModeEnabled(),
                 PrefServiceBridge.getInstance().isIncognitoModeManaged());
         mActivity.prepareMenu(menu);