In BrowserAccessibility, there are at least two sets of functions that walk the ax tree.  We should clean up class up a bit, move methods into groups, and document the different sets of walkers.  The first set is prefixed with Internal* and the second set is prefixed with Platform*.

Internal* methods will cross frame boundaries as well as show all items in the tree regardless if they are exposed to the rest of the system.  These APIs probably should be private.

Platform* methods do not cross frame boundaries and limit what they expose when walking the AX tree.