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When orthogonal writing mode roots have floating siblings, its
containing block may still have old or even deleted LayoutObjects.
This occurs when LayoutMultiColumnFlowThread::populate(),
LayoutBoxModelObject::moveChildrenTo() with !fullRemoveInsert,
or more, for the optimization purposes.

This patch clears such objects to be re-created when the containing
block is laid out.

BUG=604095, 633409, 646178

Review-Url: https://codereview.chromium.org/2025543002
Cr-Commit-Position: refs/heads/master@{#419376}