Fix bug in keeping capture in sync during destruction

ui/aura/mus/capture_synchronizer.h

Index: ui/aura/mus/capture_synchronizer.h
diff --git a/ui/aura/mus/capture_synchronizer.h b/ui/aura/mus/capture_synchronizer.h
new file mode 100644
index 0000000000000000000000000000000000000000..87bce872168d8c50d69ab3361b1d2643d8affb9b
--- /dev/null
+++ b/ui/aura/mus/capture_synchronizer.h
@@ -0,0 +1,74 @@
+// 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 UI_AURA_MUS_CAPTURE_SYNCHRONIZER_H_
+#define UI_AURA_MUS_CAPTURE_SYNCHRONIZER_H_
+
+#include <stdint.h>
+
+#include "base/macros.h"
+#include "ui/aura/aura_export.h"
+#include "ui/aura/client/capture_client_observer.h"
+#include "ui/aura/window_observer.h"
+
+namespace ui {
+namespace mojom {
+class WindowTree;
+}
+}
+
+namespace aura {
+class CaptureSynchronizerDelegate;
+class WindowMus;
+
+namespace client {
+class CaptureClient;
+}
+
+// CaptureSynchronizer is resonsible for keeping capture in sync between aura
+// and the mus server.
+class CaptureSynchronizer : public WindowObserver,
+                            public client::CaptureClientObserver {
+ public:
+  CaptureSynchronizer(CaptureSynchronizerDelegate* delegate,
+                      ui::mojom::WindowTree* window_tree,
+                      client::CaptureClient* capture_client);
+  ~CaptureSynchronizer() override;
+
+  WindowMus* capture_window() { return capture_window_; }
+
+  // Called when the server side wants to change capture to |window|.
+  void SetCaptureFromServer(WindowMus* window);
+
+ private:
+  // Internal implementation for capture changes. Adds/removes observer as
+  // necessary and sets |capture_window_| to |window|.
+  void SetCaptureWindow(WindowMus* window);
+
+  // WindowObserver:
+  void OnWindowDestroying(Window* window) override;
+
+  // client::CaptureClientObserver:
+  void OnCaptureChanged(Window* lost_capture, Window* gained_capture) override;
+
+  CaptureSynchronizerDelegate* delegate_;
+  ui::mojom::WindowTree* window_tree_;
+  client::CaptureClient* capture_client_;
+
+  // Window that currently has capture.
+  WindowMus* capture_window_ = nullptr;
+
+  // Used when setting capture from the server to avoid setting capture back
+  // on the server. If |setting_capture_| is true SetCaptureFromServer() was
+  // called and |window_setting_capture_to_| is the window capture is being
+  // set on.
+  bool setting_capture_ = false;
+  WindowMus* window_setting_capture_to_ = nullptr;
+
+  DISALLOW_COPY_AND_ASSIGN(CaptureSynchronizer);
+};
+
+}  // namespace aura
+
+#endif  // UI_AURA_MUS_CAPTURE_SYNCHRONIZER_H_