Remove dependency on //build/config/linux/gtk

I'm planning on removing //build/config/linux/gtk in Chrome, so this
CL removes the dep in WebRTC.

Bug: None
Change-Id: I8b644ae38402335ba98fc4bf9932d132b6c816b4
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/258261
Auto-Submit: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36514}

examples/BUILD.gn

@@ -15,6 +15,8 @@ if (is_android) {
   import("//build/config/mac/rules.gni")
 } else if (is_ios) {
   import("//build/config/ios/rules.gni")
+} else if (is_linux || is_chromeos) {
+  import("//build/config/linux/pkg_config.gni")
 }
 
 group("examples") {
@@ -660,6 +662,18 @@ if (is_ios || (is_mac && target_cpu != "x86")) {
 }
 
 if (is_linux || is_chromeos || is_win) {
+  if (is_linux || is_chromeos) {
+    pkg_config("gtk_config") {
+      packages = [
+        # Gtk requires gmodule, but it does not list it as a dependency in some
+        # misconfigured systems.
+        "gmodule-2.0",
+        "gthread-2.0",
+        "gtk+-3.0",
+      ]
+    }
+  }
+
   rtc_executable("peerconnection_client") {
     testonly = true
     sources = [
@@ -726,7 +740,7 @@ if (is_linux || is_chromeos || is_win) {
         "Xext",
         "Xrender",
       ]
-      deps += [ "//build/config/linux/gtk" ]
+      configs += [ ":gtk_config" ]
     }
 
     deps += [

examples/peerconnection/client/linux/main_wnd.cc

@@ -264,20 +264,12 @@ void GtkMainWnd::SwitchToConnectUI() {
     peer_list_ = NULL;
   }
 
-#if GTK_MAJOR_VERSION == 2
-  vbox_ = gtk_vbox_new(FALSE, 5);
-#else
   vbox_ = gtk_box_new(GTK_ORIENTATION_VERTICAL, 5);
-#endif
   GtkWidget* valign = gtk_alignment_new(0, 1, 0, 0);
   gtk_container_add(GTK_CONTAINER(vbox_), valign);
   gtk_container_add(GTK_CONTAINER(window_), vbox_);
 
-#if GTK_MAJOR_VERSION == 2
-  GtkWidget* hbox = gtk_hbox_new(FALSE, 5);
-#else
   GtkWidget* hbox = gtk_box_new(GTK_ORIENTATION_HORIZONTAL, 5);
-#endif
 
   GtkWidget* label = gtk_label_new("Server");
   gtk_container_add(GTK_CONTAINER(hbox), label);
@@ -386,11 +378,7 @@ void GtkMainWnd::OnClicked(GtkWidget* widget) {
 void GtkMainWnd::OnKeyPress(GtkWidget* widget, GdkEventKey* key) {
   if (key->type == GDK_KEY_PRESS) {
     switch (key->keyval) {
-#if GTK_MAJOR_VERSION == 2
-      case GDK_Escape:
-#else
       case GDK_KEY_Escape:
-#endif
         if (draw_area_) {
           callback_->DisconnectFromCurrentPeer();
         } else if (peer_list_) {
@@ -398,13 +386,8 @@ void GtkMainWnd::OnKeyPress(GtkWidget* widget, GdkEventKey* key) {
         }
         break;
 
-#if GTK_MAJOR_VERSION == 2
-      case GDK_KP_Enter:
-      case GDK_Return:
-#else
       case GDK_KEY_KP_Enter:
       case GDK_KEY_Return:
-#endif
         if (vbox_) {
           OnClicked(NULL);
         } else if (peer_list_) {
@@ -490,21 +473,13 @@ void GtkMainWnd::OnRedraw() {
       }
     }
 
-#if GTK_MAJOR_VERSION == 2
-    gdk_draw_rgb_32_image(draw_area_->window,
-                          draw_area_->style->fg_gc[GTK_STATE_NORMAL], 0, 0,
-                          width_ * 2, height_ * 2, GDK_RGB_DITHER_MAX,
-                          draw_buffer_.get(), (width_ * 2) * 4);
-#else
     gtk_widget_queue_draw(draw_area_);
-#endif
   }
 
   gdk_threads_leave();
 }
 
 void GtkMainWnd::Draw(GtkWidget* widget, cairo_t* cr) {
-#if GTK_MAJOR_VERSION != 2
   cairo_format_t format = CAIRO_FORMAT_ARGB32;
   cairo_surface_t* surface = cairo_image_surface_create_for_data(
       draw_buffer_.get(), format, width_ * 2, height_ * 2,
@@ -513,9 +488,6 @@ void GtkMainWnd::Draw(GtkWidget* widget, cairo_t* cr) {
   cairo_rectangle(cr, 0, 0, width_ * 2, height_ * 2);
   cairo_fill(cr);
   cairo_surface_destroy(surface);
-#else
-  RTC_DCHECK_NOTREACHED();
-#endif
 }
 
 GtkMainWnd::VideoRenderer::VideoRenderer(