Call CompositorViewHolder#onContentChanged when hiding Start

If the Start Surface was showing, the ContentView for the currently
selected Tab behind the Start Surface may not yet be attached and
therefore the Tab may not be interactive. Notify CompositorViewHolder
that content has changed when hiding Start for an inbound View intent, which will cause the Tab's ContentView to be attached.

Bug: 1457603
Change-Id: I7b7e999163e674badb0b44ea4f5d0c1e960967eb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4776263
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Commit-Queue: Theresa Sullivan <twellington@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1182804}