STR: 1. Load the testcase and enable paint flashing. 2. Move your mouse over the box with the black border. Expected results: Only the blue box should be layerized and invalidated. Actual results: The green box is invalidated, too. Animating the blue box causes the green box to get its own layer because our code thinks that the blue box might move under it. But that's not possible because the blue box is clipped by the black box.

Backed out for B2G reftest failures (is quite likely just bug 1024473, but the tree has been closed for too long for a variety of other things to find out the hard way :-)): https://tbpl.mozilla.org/php/getParsedLog.php?id=42435769&tree=Mozilla-Inbound remote: https://hg.mozilla.org/integration/mozilla-inbound/rev/67b3cf32b1ad remote: https://hg.mozilla.org/integration/mozilla-inbound/rev/8592e4efd83a remote: https://hg.mozilla.org/integration/mozilla-inbound/rev/6cce72f71152