ScreenCapture for Android phase1, part I

content/browser/media/capture/screen_capture_device_android.h

+// 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 CONTENT_BROWSER_MEDIA_CAPTURE_SCREEN_CAPTURE_DEVICE_ANDROID_H_
+#define CONTENT_BROWSER_MEDIA_CAPTURE_SCREEN_CAPTURE_DEVICE_ANDROID_H_
+
+#include <memory>
+
+#include "content/public/browser/power_save_blocker_factory.h"
+#include "media/capture/content/screen_capture_device_core.h"
+#include "media/capture/video/video_capture_device.h"
+
+namespace content {
+
+// ScreenCaptureDeviceAndroid is a forwarder to media::ScreenCaptureDeviceCore
+// while keeping the Power Saving from kicking in between AllocateAndStart() and
+// StopAndDeAllocate().
+class ScreenCaptureDeviceAndroid : public media::VideoCaptureDevice {
+ public:
+  ScreenCaptureDeviceAndroid();
+  ~ScreenCaptureDeviceAndroid() override;
+
+  static std::unique_ptr<media::VideoCaptureDevice> Create();

[miu, 2016/06/02 22:33:51]

This Create() function is superfluous. Please remove it, since otherwise it
infers that something more than simple construction is occurring.

[braveyao, 2016/06/08 20:39:33]

Done.

+
+  // VideoCaptureDevice implementation.
+  void AllocateAndStart(const media::VideoCaptureParams& params,
+                        std::unique_ptr<Client> client) override;
+  void StopAndDeAllocate() override;
+  void RequestRefreshFrame() override;
+
+ private:
+  media::ScreenCaptureDeviceCore core_;
+
+  std::unique_ptr<PowerSaveBlocker> power_save_blocker_;

[miu, 2016/06/02 22:33:51]

I missed part of the discussion: Why is the capture device creating/owning a
PowerSaveBlocker?

For other screen mirroring implementations, we usually instantiate a
PowerSaveBlocker only when remoting the content (i.e., when a WebRTC
PeerConnection is opened). So, is this needed here?

[braveyao, 2016/06/08 20:39:33]

The aura_window_capture_machine.cc (and desktop_capture_device.cc, kind of) does
same, I suppose. PowerSaveBlocker is only instantiated when a stream of screen
is requested for a peerconnection here too. 
Any better suggestion?

[miu, 2016/06/08 21:06:49]

Seems the PowerSaveBlocker should be instantiated by the PeerConnection (IIRC,
it already is). The question is whether there are non-PeerConnection use cases
where we'd want the blocker.

IMHO, this is something the consumer should do. Meaning, the application would
know whether the screen should be kept turned on and so code elsewhere should be
responsible for instantiating a blocker. Said another way, the capturer cannot
assume a "controller" role in the application.

[braveyao, 2016/06/08 22:49:50]

Done.
You are right. Peerconnection does it somewhere (Try to figure out.
media_web_contents_observer.cc?).

+
+  DISALLOW_COPY_AND_ASSIGN(ScreenCaptureDeviceAndroid);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_MEDIA_CAPTURE_SCREEN_CAPTURE_DEVICE_ANDROID_H_