Recreate tab switcher stacks/lists when tabs are merged

If tabs from two instances of are merged while either the StackLayout
or OverviewListLayout is active, recreate the view so that the merged
tabs show up in the layout.

BUG=602498

Review-Url: https://codereview.chromium.org/2162243002
Cr-Commit-Position: refs/heads/master@{#406945}
5 files changed