Gtk3: Whitelist X11 backend

chrome/browser/ui/libgtkui/gtk_ui.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/libgtkui/gtk_ui.h"
 
+#include <X11/Xcursor/Xcursor.h>
+#include <dlfcn.h>
 #include <math.h>
 #include <pango/pango.h>
-#include <X11/Xcursor/Xcursor.h>
 
 #include <cmath>
 #include <set>
 #include <utility>
 
 #include "base/command_line.h"
 #include "base/debug/leak_annotations.h"
 #include "base/environment.h"
 #include "base/i18n/rtl.h"
 #include "base/logging.h"
@@ skipping 349 matching lines @@
   HSL border;
   SkColorToHSL(default_color, &border);
   border.l = l;
   return HSLToSkColor(border, a * 0xff);
 }
 #endif
 
 }  // namespace
 
 GtkUi::GtkUi() : middle_click_action_(GetDefaultMiddleClickAction()) {
+#if GTK_MAJOR_VERSION > 2
+  // Force Gtk to use Xwayland if it would have used wayland.  libgtkui assumes
+  // the use of X11 (eg. X11InputMethodContextImplGtk) and will crash under
+  // other backends.
+  // TODO(thomasanderson): Change this logic once Wayland support is added.
+  static auto* _gdk_set_allowed_backends =
+      reinterpret_cast<void (*)(const gchar*)>(
+          dlsym(GetGdkSharedLibrary(), "gdk_set_allowed_backends"));
+  if (GtkVersionCheck(3, 10))
+    DCHECK(_gdk_set_allowed_backends);
+  if (_gdk_set_allowed_backends)
+    _gdk_set_allowed_backends("x11");
+#endif
   GtkInitFromCommandLine(*base::CommandLine::ForCurrentProcess());
 #if GTK_MAJOR_VERSION == 2
   native_theme_ = NativeThemeGtk2::instance();
   fake_window_ = chrome_gtk_frame_new();
   gtk_widget_realize(fake_window_);  // Is this necessary?
 #elif GTK_MAJOR_VERSION == 3
   native_theme_ = NativeThemeGtk3::instance();
   (void)fake_window_;  // Silence the unused warning.
 #else
 #error "Unsupported GTK version"
@@ skipping 638 matching lines @@
 
 float GtkUi::GetDeviceScaleFactor() const {
   return device_scale_factor_;
 }
 
 }  // namespace libgtkui
 
 views::LinuxUI* BuildGtkUi() {
   return new libgtkui::GtkUi;
 }