Remove WmLookup.

ash/common/wm_lookup.cc

Index: ash/common/wm_lookup.cc
diff --git a/ash/common/wm_lookup.cc b/ash/common/wm_lookup.cc
deleted file mode 100644
index 26319af7da2adc7289a2ba114ee924b6ec95ce1d..0000000000000000000000000000000000000000
--- a/ash/common/wm_lookup.cc
+++ /dev/null
@@ -1,22 +0,0 @@
-// Copyright 2016 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include "ash/common/wm_lookup.h"
-
-namespace ash {
-
-// static
-WmLookup* WmLookup::instance_ = nullptr;
-
-// static
-void WmLookup::Set(WmLookup* lookup) {
-  instance_ = lookup;
-}
-
-// static
-WmLookup* WmLookup::Get() {
-  return instance_;
-}
-
-}  // namespace ash