Fix mistaken assumptions in tests

This test assumes that spinning the event loop is sufficient to trigger
asynchronous style recalculation. After we move style recalculation to be
triggered off requestAnimationFrame, this assumption will no longer be valid.
This CL removes this assumption by triggering layout explicitly

R=fsamuel@chromium.org
BUG=337617

Review URL: https://codereview.chromium.org/148153013

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247563 0039d316-1c4b-4281-b951-d872f2087c98
Protect AppListItemList Add/Remove and fix sync bugs

This should fixe the issues seen in the bug, and includes some cleanup
in prep for syncing folders.

BUG=338520
TBR=jamescook@chromium.org for ash_shell.cc

Review URL: https://codereview.chromium.org/148403007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247565 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247565