Case: invoke load() on an element should resolve pending promises in order.
Expected result: the pending promises are resolved in order.
MozReview-Commit-ID: 1FSdBd3zwrB
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extra : rebase_source : fddd8742d80b68fced9ac9c09f8d918af4e6bba7
extra : source : 9c0a4abd7ff8ebffc1fc4369a335be299b8ba3dd