Change Cell Border Width

Changing a cell's collapsed border's width should change the width of the sibling cells and the table.

There should be 3 squares. Outer two are lime, middle one is blue with a lightblue border.

Firefox 50.0a1 (nightly 2016-07-19) fails this, so it should probably be upstreamed, except it uses chrome-specific runAfterLayoutAndPaint.

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