Bug 972713. Part 1: Make all callers of GetAnimatedGeometryRootFor pass a display item so we can stop searching when we reach the item's reference frame. r=mattwoodrow
This guarantees that the animated geometry root for an item is always in the
same display list coordinate system as the frame.

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extra : rebase_source : 249fd847a2c08f8d0846d698cce9dd4681e38a98
Bug 972713. Part 2: Ignore active scrolled roots in inactive layer trees, because they don't help and could hurt. r=mattwoodrow