Makes ash/wm/common a library

ash/wm/aura/wm_lookup_aura.h

Index: ash/wm/aura/wm_lookup_aura.h
diff --git a/ash/wm/aura/wm_lookup_aura.h b/ash/wm/aura/wm_lookup_aura.h
new file mode 100644
index 0000000000000000000000000000000000000000..572ff719ce87f916e4c2ec413217bb5a373d05cb
--- /dev/null
+++ b/ash/wm/aura/wm_lookup_aura.h
@@ -0,0 +1,32 @@
+// 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_AURA_WM_LOOKUP_AURA_H_
+#define ASH_WM_AURA_WM_LOOKUP_AURA_H_
+
+#include "ash/wm/common/wm_lookup.h"
+#include "base/macros.h"
+
+namespace ash {
+namespace wm {
+
+// Aura implementation of WmLookup.
+class WmLookupAura : public WmLookup {
+ public:
+  WmLookupAura();
+  ~WmLookupAura() override;
+
+  // WmLookup:
+  WmRootWindowController* GetRootWindowControllerWithDisplayId(
+      int64_t id) override;
+  WmWindow* GetWindowForWidget(views::Widget* widget) override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(WmLookupAura);
+};
+
+}  // namespace wm
+}  // namespace ash
+
+#endif  // ASH_WM_AURA_WM_LOOKUP_AURA_H_