Add support for screen sharing with PipeWire on Wayland

Currently, when users want to use the screen sharing and are using the
Wayland display server (the default on Fedora distribution), then it
doesn't work, because the WebRTC only includes the X11 implementation.
This change adds the support by using the PipeWire multimedia server.

The PipeWire implementation in WebRTC stays in
screen-capturer-pipewire.c and is guarded by the rtc_use_pipewire build
flag that is automatically enabled on Linux.

More information are included in the relevant commit messages.

Tested on the current Chromium master and Firefox.

The sysroot changes are requested in:
https://chromium-review.googlesource.com/c/chromium/src/+/1258174

Co-authored-by: Jan Grulich <grulja@gmail.com>
Co-authored-by: Eike Rathke <erathke@redhat.com>
Change-Id: I212074a4bc437b99a77bf383266026c5bfae7c4a

BUG=chromium:682122

Change-Id: I212074a4bc437b99a77bf383266026c5bfae7c4a
Reviewed-on: https://webrtc-review.googlesource.com/c/103504
Commit-Queue: Patrik Höglund <phoglund@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Reviewed-by: Brave Yao <braveyao@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25461}

modules/desktop_capture/linux/x_server_pixel_buffer.h

@@ -0,0 +1,84 @@
+/*
+ *  Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+// Don't include this file in any .h files because it pulls in some X headers.
+
+#ifndef MODULES_DESKTOP_CAPTURE_LINUX_X_SERVER_PIXEL_BUFFER_H_
+#define MODULES_DESKTOP_CAPTURE_LINUX_X_SERVER_PIXEL_BUFFER_H_
+
+#include <X11/Xutil.h>
+#include <X11/extensions/XShm.h>
+
+#include "modules/desktop_capture/desktop_geometry.h"
+#include "rtc_base/constructormagic.h"
+
+namespace webrtc {
+
+class DesktopFrame;
+
+// A class to allow the X server's pixel buffer to be accessed as efficiently
+// as possible.
+class XServerPixelBuffer {
+ public:
+  XServerPixelBuffer();
+  ~XServerPixelBuffer();
+
+  void Release();
+
+  // Allocate (or reallocate) the pixel buffer for |window|. Returns false in
+  // case of an error (e.g. window doesn't exist).
+  bool Init(Display* display, Window window);
+
+  bool is_initialized() { return window_ != 0; }
+
+  // Returns the size of the window the buffer was initialized for.
+  DesktopSize window_size() { return window_rect_.size(); }
+
+  // Returns the rectangle of the window the buffer was initialized for.
+  const DesktopRect& window_rect() { return window_rect_; }
+
+  // Returns true if the window can be found.
+  bool IsWindowValid() const;
+
+  // If shared memory is being used without pixmaps, synchronize this pixel
+  // buffer with the root window contents (otherwise, this is a no-op).
+  // This is to avoid doing a full-screen capture for each individual
+  // rectangle in the capture list, when it only needs to be done once at the
+  // beginning.
+  void Synchronize();
+
+  // Capture the specified rectangle and stores it in the |frame|. In the case
+  // where the full-screen data is captured by Synchronize(), this simply
+  // returns the pointer without doing any more work. The caller must ensure
+  // that |rect| is not larger than window_size().
+  bool CaptureRect(const DesktopRect& rect, DesktopFrame* frame);
+
+ private:
+  void ReleaseSharedMemorySegment();
+
+  void InitShm(const XWindowAttributes& attributes);
+  bool InitPixmaps(int depth);
+
+  Display* display_ = nullptr;
+  Window window_ = 0;
+  DesktopRect window_rect_;
+  XImage* x_image_ = nullptr;
+  XShmSegmentInfo* shm_segment_info_ = nullptr;
+  XImage* x_shm_image_ = nullptr;
+  Pixmap shm_pixmap_ = 0;
+  GC shm_gc_ = nullptr;
+  bool xshm_get_image_succeeded_ = false;
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(XServerPixelBuffer);
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_DESKTOP_CAPTURE_LINUX_X_SERVER_PIXEL_BUFFER_H_