Add a gtk3 port of peerconnection_client on Linux

webrtc/examples/peerconnection/client/linux/main_wnd.h

Index: webrtc/examples/peerconnection/client/linux/main_wnd.h
diff --git a/webrtc/examples/peerconnection/client/linux/main_wnd.h b/webrtc/examples/peerconnection/client/linux/main_wnd.h
index 33b0725c08898bb3cfa98a8680466b6472c63d2c..68ed8bf99caf1bd489166b1049b916d2fe3fa13e 100644
--- a/webrtc/examples/peerconnection/client/linux/main_wnd.h
+++ b/webrtc/examples/peerconnection/client/linux/main_wnd.h
@@ -24,6 +24,7 @@ typedef struct _GdkEventKey GdkEventKey;
 typedef struct _GtkTreeView GtkTreeView;
 typedef struct _GtkTreePath GtkTreePath;
 typedef struct _GtkTreeViewColumn GtkTreeViewColumn;
+typedef struct _cairo cairo_t;
 
 // Implements the main UI of the peer connection client.
 // This is functionally equivalent to the MainWnd class in the Windows
@@ -71,6 +72,8 @@ class GtkMainWnd : public MainWindow {
 
   void OnRedraw();
 
+  void Draw(GtkWidget* widget, cairo_t* cr);
+
  protected:
   class VideoRenderer : public rtc::VideoSinkInterface<webrtc::VideoFrame> {
    public:
@@ -114,6 +117,8 @@ class GtkMainWnd : public MainWindow {
   bool autocall_;
   std::unique_ptr<VideoRenderer> local_renderer_;
   std::unique_ptr<VideoRenderer> remote_renderer_;
+  int width_;
+  int height_;
   std::unique_ptr<uint8_t[]> draw_buffer_;
   int draw_buffer_size_;
 };