Rename apps::ShellWindow to apps::AppWindow

* Rename ShellWindowRegistry
* Rename ShellWindowGeometryCache
* Rename members like shell_window_ to app_window_
* Rename locals like shell_window to app_window

BUG=343591
TEST=compiles
COLLABORATOR=scheib@chromium.org
TBR=skuhne@chromium.org for chrome/browser/ui/ash/launcher
TBR=thakis@chromium.org for chrome/browser/ui/cocoa
TBR=erg@chromium.org for chrome/browser/ui/gtk
TBR=sky@chromium.org for chrome/test

Review URL: https://codereview.chromium.org/166573005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251542 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251542