[Toolbar] Re-enable ToolbarButtonTest.

BUG=325055

Review URL: https://codereview.chromium.org/113093002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240210 0039d316-1c4b-4281-b951-d872f2087c98
Implement ScreenTrayItem::UpdateAfterShelfAlignmentChange()

Center the screen tray item based on shelf alignment.

BUG=322131
TEST=verify visually that screen sharing/capture icon is centered.
R=stevenjb@chromium.org

Review URL: https://codereview.chromium.org/103813004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240212 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240210
SVN changes up to revision 240212