WebView's scrollBarStyle need to be set at init

At initialization time of WebView, the View's scrollBarStyle is set
according to the xml file.
But WebView didn't pick that info up to specialize its own variable.

The fix is to call WebView's setScrollBarStyle according to the View's
ScrollBarStyle at the init() time.
This will help Gmail to pick up the scrollBarStyle from xml file
correctly.

bug:3409308

Change-Id: I3792b12a36bd989b6c31e0054ebacce4269300da