Auto merge of #982 - demo99:scroll_layer_id, r=mrobinson
Auto merge of #982 - demo99:scroll_layer_id, r=mrobinson

Correct scroll layer id in push_built_display_list.

There is an issue[1] about using push_built_display_list in gecko. Setting current scroll_layer_id to the items in built display list can fix the problem.

[1] https://bugzilla.mozilla.org/show_bug.cgi?id=1346915

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