Refactors DimWindow and moves to ash/common

ash/common/wm_window_user_data.h

Index: ash/common/wm_window_user_data.h
diff --git a/ash/common/wm_window_user_data.h b/ash/common/wm_window_user_data.h
new file mode 100644
index 0000000000000000000000000000000000000000..bafd19faf347af44e9751b57b82d2f5f3c3ee398
--- /dev/null
+++ b/ash/common/wm_window_user_data.h
@@ -0,0 +1,77 @@
+// 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_COMMON_WM_WINDOW_USER_DATA_H_
+#define ASH_COMMON_WM_WINDOW_USER_DATA_H_
+
+#include <map>
+#include <memory>
+#include <utility>
+
+#include "ash/common/wm_window.h"
+#include "ash/common/wm_window_observer.h"
+#include "base/macros.h"
+
+namespace ash {
+
+// WmWindowUserData provides a way to associate arbitrary objects with a
+// WmWindow. WmWindowUserData owns the data, deleting it either when
+// WmWindowUserData is deleted, or when the window the data is associated with
+// is destroyed (from WmWindowObserver::OnWindowDestroying()).
+template <typename UserData>
+class WmWindowUserData : public WmWindowObserver {
+ public:
+  WmWindowUserData() {}
+
+  ~WmWindowUserData() override { clear(); }
+
+  void clear() {
+    for (auto& pair : window_to_data_)
+      pair.first->RemoveObserver(this);
+    window_to_data_.clear();
+  }
+
+  // Sets the data associated with window. This destroys any existing data.
+  // |data| may be null.
+  void Set(WmWindow* window, std::unique_ptr<UserData> data) {
+    if (!data) {
+      if (window_to_data_.erase(window))
+        window->RemoveObserver(this);
+      return;
+    }
+    if (window_to_data_.count(window) == 0u)
+      window->AddObserver(this);
+    window_to_data_[window] = std::move(data);
+  }
+
+  // Returns the data associated with the window, or null if none set. The
+  // returned object is owned by WmWindowUserData.
+  UserData* Get(WmWindow* window) {
+    auto it = window_to_data_.find(window);
+    return it == window_to_data_.end() ? nullptr : it->second.get();
+  }
+
+  // Returns the set of windows with data associated with them.
+  std::set<WmWindow*> GetWindows() {
+    std::set<WmWindow*> windows;
+    for (auto& pair : window_to_data_)
+      windows.insert(pair.first);
+    return windows;
+  }
+
+ private:
+  // WmWindowObserver:
+  void OnWindowDestroying(WmWindow* window) override {
+    window->RemoveObserver(this);
+    window_to_data_.erase(window);
+  }
+
+  std::map<WmWindow*, std::unique_ptr<UserData>> window_to_data_;
+
+  DISALLOW_COPY_AND_ASSIGN(WmWindowUserData);
+};
+
+}  // namespace ash
+
+#endif  // ASH_COMMON_WM_WINDOW_USER_DATA_H_