[win8] Ignore non-Ash ShellWindows in Ash's ShellWindowLauncherController

Currently if a packaged app is running in desktop mode, and it is
launched again from the Ash Desktop on Windows 8, Ash will try to focus
the currently running app on the (hidden) Windows Desktop.

This change allows the Ash desktop to open its own copy of packaged apps
that support being launched multiple times.

BUG=288251
TEST=Open a packaged app in desktop mode that supports multiple windows
(e.g. 500px, "Hex Lines"). Leave it open, and open the same app in
Windows 8/Ash mode. A new window should open in Ash. Note that
"singleton" apps  that specify an id when creating windows (e.g. Google
Keep) are not yet fixed by this.

Review URL: https://codereview.chromium.org/28913003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230322 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230322