Sends OOP drop events to content analysis for approval before sending them to
the DOM. It intercepts drop events at the browser level and sends them to CA
before calling stopPropagation and preventDefault on them. (CA also presents a
modal dialog over the tab.) The drag session then ends as usual in the parent
process but remains open on the related browser in the process where it would be
sent to the DOM while the drop is being analyzed. While CA runs, the browser
dispatches an eQueryDropTargetHittest event to locate the drop target while the
event screen coordinates are still valid. When CA is complete, a drop or
dragexit event is sent to the drop target (drop if it was approved by CA). Calls
to EndDragSession are delayed during this.
Differential Revision: https://phabricator.services.mozilla.com/D219201
2f776696c6