-Temporarily add setting override width as well so that we correctly bypass in RenderBox::computeLogicalWidth.
-Add setNeedsLayout so that the author code can force layouts (e.g. when the container's width changes).
-Have setLayoutManager force a reattach of the element if it's renderer wasn't a custom layout one before.
-Remove the laying out of children from RenderCustomLayout::layout. This is the job of the author code.
-Add a test case.
R=eseidel@chromium.org
Review URL: https://codereview.chromium.org/1055263002
08dbc60abd