Fix position fixed handling is iOS <= 4_2

Seems to need to account for the height of the address bar
and the open keyboard

Cleanup user agent testing in process
Bug: 53048

Change-Id: I841ca5c6925ff189bd7a9b24e04d645d491dbf1f
Beta: Open sections by default in tablet view

Change-Id: I507b0cf9faca49bcb4a92bb45cf7dd68874487e1