Add CreateWindowCapturer() and CreateScreenCapturer() in DesktopCapturer

webrtc/modules/desktop_capture/window_capturer_x11.cc

Index: webrtc/modules/desktop_capture/window_capturer_x11.cc
diff --git a/webrtc/modules/desktop_capture/window_capturer_x11.cc b/webrtc/modules/desktop_capture/window_capturer_x11.cc
index 2e2ce9bba991f447fc5af36cdc32403b1ce862dd..11a27d52c2f81d559b4013593eaf44c000dd0b74 100644
--- a/webrtc/modules/desktop_capture/window_capturer_x11.cc
+++ b/webrtc/modules/desktop_capture/window_capturer_x11.cc
@@ -430,4 +430,12 @@ WindowCapturer* WindowCapturer::Create(const DesktopCaptureOptions& options) {
   return new WindowCapturerLinux(options);
 }
 
+// static
+std::unique_ptr<DesktopCapturer> DesktopCapturer::CreateRawWindowCapturer(
+    const DesktopCaptureOptions& options) {
+  if (!options.x_display())
+    return nullptr;
+  return std::unique_ptr<DesktopCapturer>(new WindowCapturerLinux(options));
+}
+
 }  // namespace webrtc