change the way windows are parented when their parent is set to NULL.

Changes the way windows are parented when their parent is set to NULL.. Adds a DesktopDelegate interface implemented by the aura client. The implementor handles parenting of windows when their parent is set to NULL, and also figures out how to activate windows.. Replaces Desktop::default_parent() with this. Requires adjusting some of the tests and adding a TestDesktopDelegate implementation that reconstructs what default_parent did.BUG=noneTEST=existing unit tests
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=104558

[sky, 2011-10-07 19:59:45]

LGTM

http://codereview.chromium.org/8194004/diff/6046/ui/aura/test_desktop_delegat...
File ui/aura/test_desktop_delegate.cc (right):

http://codereview.chromium.org/8194004/diff/6046/ui/aura/test_desktop_delegat...
ui/aura/test_desktop_delegate.cc:13: Desktop::GetInstance()->set_delegate(this);
Unset in the destructor?

http://codereview.chromium.org/8194004/diff/6046/ui/aura/test_desktop_delegat...
ui/aura/test_desktop_delegate.cc:24: 
nit: remove one of these.

http://codereview.chromium.org/8194004/diff/6046/ui/aura/toplevel_window_cont...
File ui/aura/toplevel_window_container.h (right):

http://codereview.chromium.org/8194004/diff/6046/ui/aura/toplevel_window_cont...
ui/aura/toplevel_window_container.h:26: OVERRIDE;
nit: wrap function name to avoid dangling OVERRIDE.

http://codereview.chromium.org/8194004/diff/6046/ui/aura/window.h
File ui/aura/window.h (right):

http://codereview.chromium.org/8194004/diff/6046/ui/aura/window.h#newcode55
ui/aura/window.h:55: int type() const { return type_; }
Add a description of what this is and who uses it.

http://codereview.chromium.org/8194004/diff/6046/ui/aura_shell/shell.h
File ui/aura_shell/shell.h (right):

http://codereview.chromium.org/8194004/diff/6046/ui/aura_shell/shell.h#newcode19
ui/aura_shell/shell.h:19: class Shell : public aura::DesktopDelegate {
Add a description