Merge pull request #24899 from etiennesegonzac/bug-1079379

Bug 1079379 - Decode the screenshots "as we go" while edge swiping. r=aus
(cherry picked from commit 76122f7ba317cf2aa7a091cb4512ca8ce69335b9)

Conflicts:
	apps/system/js/app_window.js
	apps/system/test/unit/app_window_test.js