Fix a crash when creating an incognito tab.

The KitKat's WebView doesn't support an incognito mode.
Opening an incognito tab leads to a crash.
So it would be nice to hide the menu itself in the KitKat or later.

Change-Id: I9853df92f3a4e404b528640776725b34b675fee5
Signed-off-by: Sungmann Cho <sungmann.cho@navercorp.com>