Implement "pinned" mode in ash.

ash/wm/pinned_controller.h

Index: ash/wm/pinned_controller.h
diff --git a/ash/wm/pinned_controller.h b/ash/wm/pinned_controller.h
new file mode 100644
index 0000000000000000000000000000000000000000..6c4d3e1ce7ebcebcf4c1a640506b2e73acf3a2b3
--- /dev/null
+++ b/ash/wm/pinned_controller.h
@@ -0,0 +1,70 @@
+// 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_PINNED_CONTROLLER_H_
+#define ASH_WM_PINNED_CONTROLLER_H_
+
+#include <vector>
+
+#include "ash/common/shell_observer.h"
+#include "ash/common/wm_window_observer.h"
+#include "ash/display/window_tree_host_manager.h"
+#include "base/macros.h"
+
+namespace ash {
+
+class WmWindow;
+
+namespace wm {
+
+// Handles pinned state.
+class PinnedController : public ShellObserver,
+                         public WmWindowObserver,
+                         public WindowTreeHostManager::Observer {
+ public:
+  PinnedController();
+  ~PinnedController() override;
+
+  // Returns true if in pinned mode, otherwise false.
+  bool IsPinned() const;
+
+ private:
+  // Pinned window should be on top in the parent window.
+  WmWindow* pinned_window_ = nullptr;
+  // Dim background window just behind of the pinned window.
+  // Not owned. The parent has its ownership.
+  WmWindow* background_window_ = nullptr;
+  // In pinned mode, all displays other than the one where pinned_window_ is.
+  // Similar to background_window_, not owned.
+  std::vector<WmWindow*> dim_windows_;
+  // Set true only when restacking done by this controller.
+  bool in_restacking_ = false;
+
+  // Keeps the pinned window on top of the siblings.
+  void KeepPinnedWindowOnTop();
+
+  // Keeps the dim window on top of the container.
+  void KeepDimWindowOnTop(WmWindow* container);
+
+  // ShellObserver override.
+  void OnPinnedStateChanged(WmWindow* pinned_window) override;
+
+  // WmWindowObserver override.
+  void OnWindowTreeChanging(WmWindow* window,
+                            const TreeChangeParams& params) override;
+  void OnWindowTreeChanged(WmWindow* window,
+                           const TreeChangeParams& params) override;
+  void OnWindowStackingChanged(WmWindow* window) override;
+  void OnWindowDestroying(WmWindow* window) override;
+
+  // WindowTreeHostManager::Observer override.
+  void OnDisplayConfigurationChanged() override;
+
+  DISALLOW_COPY_AND_ASSIGN(PinnedController);
+};
+
+}  // namespace wm
+}  // namespace ash
+
+#endif  // ASH_WM_PINNED_CONTROLLER_H_