Several minor improvements of DirectX capturer

webrtc/modules/desktop_capture/win/dxgi_texture_staging.h

Index: webrtc/modules/desktop_capture/win/dxgi_texture_staging.h
diff --git a/webrtc/modules/desktop_capture/win/dxgi_texture_staging.h b/webrtc/modules/desktop_capture/win/dxgi_texture_staging.h
index 2da1600122a010a452697943dda2f31a28929762..47f75fa8c13c362c7ebab26b1b6f2be563d2bbbf 100644
--- a/webrtc/modules/desktop_capture/win/dxgi_texture_staging.h
+++ b/webrtc/modules/desktop_capture/win/dxgi_texture_staging.h
@@ -58,7 +58,7 @@ class DxgiTextureStaging : public DxgiTexture {
   void AssertStageAndSurfaceAreSameObject();
 
   const DesktopRect desktop_rect_;
-  const D3dDevice& device_;

[Jamie, 2016/09/17 00:49:30]

No need for const.

[Hzj_jie, 2016/09/19 19:09:57]

Same explanation in dxgi_output_duplicator.h.

+  const D3dDevice device_;

[Sergey Ulanov, 2016/09/19 22:15:19]

I'm not sure you actually need this. Maybe just pass D3dDevice reference to
CopyFrom()?

[Hzj_jie, 2016/09/19 23:15:27]

The DxgiTextureMapping does not need to use D3dDevice at all, so the two
implementations (DxgiTextureMapping and DxgiTextureStaging) have different
constructors, but identical CopyFrom() function with the intersect of the
required parameters.

   Microsoft::WRL::ComPtr<ID3D11Texture2D> stage_;
   Microsoft::WRL::ComPtr<IDXGISurface> surface_;
 };