This bug implements and opens window.print() for Android in Nightly.
Adds "GeckoView:DotPrintRequest" and "GeckoView:DotPrintFinish" events.
GeckoView:DotPrintRequest requests a PDF of the current window.print
page for Android to print. GeckoView:DotPrintFinish releases the static
browser clone created by window.print. PDF generation was additionally
adjusted to get the expected canonical browser context when printing
iframes.
Differential Revision: https://phabricator.services.mozilla.com/D171159