add more alt key acceleration in webview

Make key accceleration exact; if alt is required,
allow only alt, and so on.

Also, set the touch point when nav'ing with the arrows
or trackball so that context menus have a point to
work with.

bug:3301564
bug:3241968
Change-Id: I574ce145941e84ac0934efd323d9db71eec11663