Makes WorkspaceWindowResizer use ash/wm/common types

ash/wm/common/wm_window_tracker.h

Index: ash/wm/common/wm_window_tracker.h
diff --git a/ash/wm/common/wm_window_tracker.h b/ash/wm/common/wm_window_tracker.h
new file mode 100644
index 0000000000000000000000000000000000000000..724a6fc048f213126f989a904e22ab5523af6fc1
--- /dev/null
+++ b/ash/wm/common/wm_window_tracker.h
@@ -0,0 +1,19 @@
+// 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.
+
+#ifndef ASH_WM_COMMON_WM_WINDOW_TRACKER_H_
+#define ASH_WM_COMMON_WM_WINDOW_TRACKER_H_
+
+#include "ash/wm/common/wm_window_observer.h"
+#include "ui/base/window_tracker_template.h"
+
+namespace ash {
+namespace wm {
+
+using WmWindowTracker = ui::WindowTrackerTemplate<WmWindow, WmWindowObserver>;
+
+}  // namespace wm
+}  // namespace ash
+
+#endif  // ASH_WM_COMMON_WM_WINDOW_TRACKER_H_