Change ImmersiveContextMus to use DesktopCaptureClient.

ui/views/widget/desktop_aura/desktop_capture_client.h

 // Copyright 2013 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_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_CAPTURE_CLIENT_H_
 #define UI_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_CAPTURE_CLIENT_H_
 
 #include <set>
 
 #include "base/compiler_specific.h"
@@ skipping 19 matching lines @@
 // capture knows which window has capture. All others think no one has
 // capture. This behavior is necessitated by Windows occassionally delivering
 // mouse events to a window other than the capture window and expecting that
 // window to get the event. If we shared the capture window on the desktop this
 // behavior would not be possible.
 class VIEWS_EXPORT DesktopCaptureClient : public aura::client::CaptureClient {
  public:
   explicit DesktopCaptureClient(aura::Window* root);
   ~DesktopCaptureClient() override;
 
+  static aura::Window* GetCaptureWindowGlobal();

[sky, 2017/01/24 23:06:08]

This name is ick! How about instead adding a function get the singleton
DesktopCaptureClient and then call GetGlobalCaptureWindow on it?

[sadrul, 2017/01/25 01:02:13]

I believe the issue is that DesktopCaptureClient is not a singleton; each
DesktopNativeWidgetAura creates its own DesktopCaptureClient [1]. We *could*
have a singleton client, but looks like the current behaviour is deliberate to
work-around some issue on Windows [2].

1:
https://cs.chromium.org/chromium/src/ui/views/widget/desktop_aura/desktop_nat...
2:
https://cs.chromium.org/chromium/src/ui/views/widget/desktop_aura/desktop_cap...

[sky, 2017/01/25 04:47:48]

D'OH! You are certainly right. As I can't think of a better name, please
document that it is exactly the same as GetGlobalCaptureWindow, but static.

+
   // Overridden from aura::client::CaptureClient:
   void SetCapture(aura::Window* window) override;
   void ReleaseCapture(aura::Window* window) override;
   aura::Window* GetCaptureWindow() override;
   aura::Window* GetGlobalCaptureWindow() override;
   void AddObserver(aura::client::CaptureClientObserver* observer) override;
   void RemoveObserver(aura::client::CaptureClientObserver* observer) override;
 
  private:
   typedef std::set<DesktopCaptureClient*> CaptureClients;
 
   aura::Window* root_;
   aura::Window* capture_window_;
 
   // Set of DesktopCaptureClients.
   static CaptureClients* capture_clients_;
 
   DISALLOW_COPY_AND_ASSIGN(DesktopCaptureClient);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_CAPTURE_CLIENT_H_