Upgrade ProfileChooserView to use LabelButtons.

Convert TextButton uses/subclasses to LabelButton.
Handle a Null border in LabelButton sizing; other cleanup.
No ProfileChooserView appearance/behavior changes expected.

BUG=155363
TEST=No behavior/appearance regressions in the profile chooser bubble with or without the about:flags "Enable new profile management system" flag set.
R=sky@chromium.org

Review URL: https://codereview.chromium.org/167343004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251624 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251624