[DesktopCapturer] FallbackDesktopCapturerWrapper and its tests

webrtc/modules/desktop_capture/desktop_capturer_differ_wrapper.h

Index: webrtc/modules/desktop_capture/desktop_capturer_differ_wrapper.h
diff --git a/webrtc/modules/desktop_capture/desktop_capturer_differ_wrapper.h b/webrtc/modules/desktop_capture/desktop_capturer_differ_wrapper.h
index 0747a4ea1fb0d55c36b535f2283c8b978409d0db..ed825dde1dc9d5241215376e3b58483097f4080e 100644
--- a/webrtc/modules/desktop_capture/desktop_capturer_differ_wrapper.h
+++ b/webrtc/modules/desktop_capture/desktop_capturer_differ_wrapper.h
@@ -26,8 +26,8 @@ namespace webrtc {
 //
 // This class marks entire frame as updated if the frame size or frame stride
 // has been changed.
-class DesktopCapturerDifferWrapper : public DesktopCapturer,
-                                     public DesktopCapturer::Callback {
+class DesktopCapturerDifferWrapper final : public DesktopCapturer,
+                                           private DesktopCapturer::Callback {

[Jamie, 2017/02/15 18:43:48]

IIRC, private inheritance is not allowed in Chromium; either make it public or
use a member variable
(https://google.github.io/styleguide/cppguide.html#Inheritance).

TBH, this feels like a legitimate use of private inheritance (a member variable
is overkill, yet there's no value in exposing the inheritance to callers), so
I'll defer to Sergey on this.

[Hzj_jie, 2017/02/15 21:20:36]

I have not noticed this guide. Since using private inheritance is actively
disallowed, I will undo the change to this file.

  public:
   // Creates a DesktopCapturerDifferWrapper with a DesktopCapturer
   // implementation, and takes its ownership.