Update XServerPixelBuffer to handle shmget() errors properly.

webrtc/modules/desktop_capture/x11/x_server_pixel_buffer.h

Index: webrtc/modules/desktop_capture/x11/x_server_pixel_buffer.h
diff --git a/webrtc/modules/desktop_capture/x11/x_server_pixel_buffer.h b/webrtc/modules/desktop_capture/x11/x_server_pixel_buffer.h
index 2a177c4ff77a67a28c784ea0578a29e24977de7e..3a60880cf8359350339a03cc67c64b505d1162df 100644
--- a/webrtc/modules/desktop_capture/x11/x_server_pixel_buffer.h
+++ b/webrtc/modules/desktop_capture/x11/x_server_pixel_buffer.h
@@ -58,6 +58,8 @@ class XServerPixelBuffer {
   bool CaptureRect(const DesktopRect& rect, DesktopFrame* frame);
 
  private:
+  void ReleaseSharedMemorySegment();
+
   void InitShm(const XWindowAttributes& attributes);
   bool InitPixmaps(int depth);