Propagate the page's screen coordinates when the top-level window moved

This fixes a regression after the 37 upgrade where the select popups
would have the wrong position. Adjust to the new behavior and also
avoid doing a mapToGlobal of the position received in InitAsPopup.

RWHV::SetBounds has been giving us screen coordinates since the
Chromium 33 update, but popup locations somehow managed to work
properly through some side-effect sorcery.

This also fixes the value of window.screen[XY] in JavaScript which
wasn't updated when the window was moved.

Change-Id: I544499bafedccfb7d389b4abc48f1386c398473f
Reviewed-by: Pierre Rossi <pierre.rossi@gmail.com>