The upcoming window tracking refactoring to Marionette will introduce
a new testing/marionette/wm.js module. It was originally the plan
to move WindowState there after it had landed, but it actually makes
sense to land any dependencies before to reduce churn in the window
tracking patches.
MozReview-Commit-ID: EpqnTYYGcmg
--HG--
extra : rebase_source : d6760feefa49c522738fd3930b339bc0af70e6a5
