Enables using the magnification API for screen capturing on Windows under a Finch experiment.

content/browser/media/capture/desktop_capture_device.h

 // Copyright (c) 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 CONTENT_BROWSER_MEDIA_CAPTURE_DESKTOP_CAPTURE_DEVICE_H_
 #define CONTENT_BROWSER_MEDIA_CAPTURE_DESKTOP_CAPTURE_DEVICE_H_
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/desktop_media_id.h"
 #include "media/video/capture/video_capture_device.h"
 #include "ui/gfx/native_widget_types.h"
 
 namespace base {
 class SequencedTaskRunner;
+class Thread;
 }  // namespace base
 
 namespace webrtc {
 class DesktopCapturer;
 }  // namespace webrtc
 
 namespace content {
 
 // DesktopCaptureDevice implements VideoCaptureDevice for screens and windows.
 // It's essentially an adapter between webrtc::DesktopCapturer and
 // VideoCaptureDevice.
 class CONTENT_EXPORT DesktopCaptureDevice : public media::VideoCaptureDevice {
  public:
   // Creates capturer for the specified |source| and then creates
   // DesktopCaptureDevice for it. May return NULL in case of a failure (e.g. if
   // requested window was destroyed).
   static scoped_ptr<media::VideoCaptureDevice> Create(
       const DesktopMediaID& source);
 
+  // Run the capturer on the |task_runner|.
   DesktopCaptureDevice(scoped_refptr<base::SequencedTaskRunner> task_runner,
                        scoped_ptr<webrtc::DesktopCapturer> desktop_capturer,
                        DesktopMediaID::Type type);
+  // Run the capturer on a dedicated thread. Needed for using the magnification
+  // API on Windows.
+  DesktopCaptureDevice(scoped_ptr<base::Thread> thread,

[Sergey Ulanov, 2014/05/05 20:10:06]

It's better to avoid overriding constructor. I suggest making constructor
private and always passing both |task_runner| and |thread|. The constructor is
called from Create() and from unittests. So you'll need to befriend this class
with DesktopCaptureDeviceTest.

+                       scoped_ptr<webrtc::DesktopCapturer> desktop_capturer,
+                       DesktopMediaID::Type type);
   virtual ~DesktopCaptureDevice();
 
   // VideoCaptureDevice interface.
   virtual void AllocateAndStart(const media::VideoCaptureParams& params,
                                 scoped_ptr<Client> client) OVERRIDE;
   virtual void StopAndDeAllocate() OVERRIDE;
 
   // Set the platform-dependent window id for the notification window.
   void SetNotificationWindowId(gfx::NativeViewId window_id);
 
  private:
   class Core;
   scoped_refptr<Core> core_;
 
   DISALLOW_COPY_AND_ASSIGN(DesktopCaptureDevice);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_MEDIA_CAPTURE_DESKTOP_CAPTURE_DEVICE_H_