Positioned element with percentage padding should recalc width when containing block changed

RenderBlock::layoutPositionedObjects usually don't recalc the width of
positioned descendants with percentage padding unless its width is changed.
For positioned elements which changed their containing block, it should be
considered as if the width of the containing block changed.

TEST=fast/block/containing-block-change-percentage-padding-width-recalc.html
BUG=427629

Review URL: https://codereview.chromium.org/684733002

git-svn-id: svn://svn.chromium.org/blink/trunk@184672 bbb929c8-8fbe-4397-9dbb-9b2b20218538