This patch adds support for a "private" window flag which can be used to
open new chrome windows in private browsing mode. It also tests to make
sure that the flag is not accessible from content. A test in the next
part makes sure that the flag is accessible from chrome.
Now that window.Components is no longer acccessible to page JS, we need a way
to access it in mochitests. So this patch provides SpecialPowers.Components,
which is the bonafide Components object for the window upon which SpecialPowers
is defined. It also provides SpecialPowers.{Cc,Ci,Cr,Cu}, which are SpecialPowers-wrapped
versions of their respective sub-objects (with the exception of Ci, which is unwrapped).
