This is instantiated now that mash creates an ash::Shell. It has some segfaults caused by assumptions that CursorManager is available, which I'm fixing. After that, the shutdown animation and shutdown itself appear to work. I suspect that screen-locking is completely broken, but that's unsurprising right now.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c6250a0ced3c3b8d41214af299502af4dfefd850

commit c6250a0ced3c3b8d41214af299502af4dfefd850
Author: derat <derat@chromium.org>
Date: Wed Jan 25 05:51:53 2017

mash: Make the power button shut the system down.

Now that ash::Shell is instantiated in mash, let
LockStateController ask powerd to shut the system down when
requested. Also fix various crashes in LockStateController
due to CursorManager being uninitialized in mash and
remove WmShell::RequestShutdown() in favor of calling
LockStateController::RequestShutdown() directly.

BUG= 679062 , 632187 

Review-Url: https://codereview.chromium.org/2652093002
Cr-Commit-Position: refs/heads/master@{#445962}

[modify] https://crrev.com/c6250a0ced3c3b8d41214af299502af4dfefd850/ash/aura/wm_shell_aura.cc
[modify] https://crrev.com/c6250a0ced3c3b8d41214af299502af4dfefd850/ash/aura/wm_shell_aura.h
[modify] https://crrev.com/c6250a0ced3c3b8d41214af299502af4dfefd850/ash/common/system/date/date_default_view.cc
[modify] https://crrev.com/c6250a0ced3c3b8d41214af299502af4dfefd850/ash/common/system/tiles/tiles_default_view.cc
[modify] https://crrev.com/c6250a0ced3c3b8d41214af299502af4dfefd850/ash/common/wm_shell.h
[modify] https://crrev.com/c6250a0ced3c3b8d41214af299502af4dfefd850/ash/mus/accelerators/accelerator_controller_unittest.cc
[modify] https://crrev.com/c6250a0ced3c3b8d41214af299502af4dfefd850/ash/mus/bridge/wm_shell_mus.cc
[modify] https://crrev.com/c6250a0ced3c3b8d41214af299502af4dfefd850/ash/mus/bridge/wm_shell_mus.h
[modify] https://crrev.com/c6250a0ced3c3b8d41214af299502af4dfefd850/ash/shell.cc
[modify] https://crrev.com/c6250a0ced3c3b8d41214af299502af4dfefd850/ash/wm/lock_state_controller.cc

I'm closing this, as it's instantiated now and I think it makes more sense to have bugs tracking the missing functionality (which I think we already have; see e.g.  issue 679450 ).