ozone, libgtkui: Properly set gdk backend in GtkUi initialization

Currently Gdk backend is auto-selected in Ozone, which leads to crashes
when, for example, ozone platform is set to x11 while the browser is
being executed in a Wayland compositor (e.g: Gnome/Wayland for example).

CL modifies GtkUi ctor to set allowed gdk backends based on the current
ozone plarform.

Bug: 1008924
Change-Id: I12163357e4d3d517c4c98672ed9db3c064c2d244
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1829319
Commit-Queue: Nick Yamane <nickdiego@igalia.com>
Reviewed-by: Robert Kroeger <rjkroege@chromium.org>
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#701575}

chrome/browser/ui/libgtkui/BUILD.gn

@@ -119,4 +119,8 @@ jumbo_component("libgtkui") {
       "//ui/gfx/x",
     ]
   }
+
+  if (use_ozone) {
+    deps += [ "//ui/ozone" ]
+  }
 }

chrome/browser/ui/libgtkui/gtk_ui.cc

@@ -75,6 +75,8 @@
 #if defined(USE_X11)
 #include "ui/gfx/x/x11.h"        // nogncheck
 #include "ui/gfx/x/x11_types.h"  // nogncheck
+#elif defined(USE_OZONE)
+#include "ui/ozone/public/ozone_platform.h"
 #endif
 
 #if BUILDFLAG(ENABLE_PRINTING)
@@ -332,11 +334,15 @@ GtkUi::GtkUi() {
       {ActionSource::kRightClick, Action::kMenu}};
 
 #if defined(USE_X11)
-  // Force Gtk to use Xwayland if it would have used wayland. In Aura/X11,
-  // libgtkui assumes the use of X11 (eg. InputMethodContextImplGtk) and will
-  // crash under other backends.
-  // TODO(thomasanderson): Change this logic once Wayland support is added.
+  // Force Gtk to use Xwayland (in case a Wayland compositor is being used).
   gdk_set_allowed_backends("x11");
+#elif defined(USE_OZONE)
+  // TODO(crbug.com/1002674): This is a temporary layering violation, supported
+  // during X11 migration to Ozone. Once LinuxUI/GtkUi is reworked to be more
+  // aligned with Ozone design, this will be moved into ozone backend code.
+  std::string ozone_platform{ui::OzonePlatform::GetPlatformName()};
+  if (ozone_platform == "x11" || ozone_platform == "wayland")
+    gdk_set_allowed_backends(ozone_platform.c_str());
 #endif
 
   // Avoid GTK initializing atk-bridge, and let AuraLinux implementation

ui/ozone/public/ozone_platform.cc

@@ -57,6 +57,11 @@ OzonePlatform* OzonePlatform::GetInstance() {
   return g_instance;
 }
 
+// static
+const char* OzonePlatform::GetPlatformName() {
+  return GetOzonePlatformName();
+}
+
 // static
 OzonePlatform* OzonePlatform::EnsureInstance() {
   if (!g_instance) {

ui/ozone/public/ozone_platform.h

@@ -138,6 +138,14 @@ class COMPONENT_EXPORT(OZONE) OzonePlatform {
 
   static OzonePlatform* GetInstance();
 
+  // Returns the current ozone platform name.
+  // TODO(crbug.com/1002674): This is temporary and meant to make it possible
+  // for higher level components to take run-time actions depending on the
+  // current ozone platform selected. Which implies in layering violations,
+  // which are tolerated during the X11 migration to Ozone and must be fixed
+  // once it is done.
+  static const char* GetPlatformName();
+
   // Factory getters to override in subclasses. The returned objects will be
   // injected into the appropriate layer at startup. Subclasses should not
   // inject these objects themselves. Ownership is retained by OzonePlatform.