Begin a host-mediated drag of item out of this app. Resolves once the host has
taken over the drag (drawn the ghost, installed the pointer-capture layer); rejects
with an ItemDragError if this app may not initiate drags (forbidden) or the
item is invalid. Only a first-party chrome app holding dnd:source may call this — a
previewed/third-party app is refused at the gate (it must not synthesize drags into
sibling apps).
Begin a host-mediated drag of
itemout of this app. Resolves once the host has taken over the drag (drawn the ghost, installed the pointer-capture layer); rejects with an ItemDragError if this app may not initiate drags (forbidden) or the item is invalid. Only a first-party chrome app holdingdnd:sourcemay call this — a previewed/third-party app is refused at the gate (it must not synthesize drags into sibling apps).