DXGI capturer highly depends on video adapter and its driver, as well as Windows
itself. I recently found it cannot work on my virtualbox instance any more,
which indicates it may not work well on some specific systems. What worse is,
the APIs do not return a failure in such case.
So this change adds a BlankDetectorDesktopCapturerWrapper, which samples several
pixels in the frame returned by a DesktopCapturer implementation. If all the
pixels selected are blank, this wrapper returns a failure. A typical usage is to
combine BlankDetectorDesktopCapturerWrapper with FallbackDesktopCapturerWrapper,
and use GDI capturer in case of failure.
Usually less than 500 pixels are checked, so the
BlankDetectorDesktopCapturerWrapper should not impact the capturer performance.
This change is expected to resolve bug 682112 in another dimension.
BUG=682112
Review-Url: https://codereview.webrtc.org/2709523003
Cr-Commit-Position: refs/heads/master@{#16984}
c4e9d210b3