Part 5 adds an assert that we always return an APZC from GetAPZCAtPoint. The test for bug 1119497 fails this assumption because it does not give it's layer tree a root AZPC. In all non-test code we ensure that there is always a root APZC and many things would break without such. So we modify the test to always have a root APZC more like actual code.
The test is testing that we don't return the layer below (with an APZC) the topmost child layer (without an APZC). So checking if we hit the root APZC still makes the test test the same thing.
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