Fix cursor theme support on Aura/X11

After https://crrev.com/c/2260642, Aura/X11 was ported to the Ozone
infraestructure for cursor loading. That meant removing CursorLoaderX11,
which implemented cursor theme changes.

In Ozone, cursor theme support was explicitly initialized after LinuxUI
was built. This CL enables the same code path for Aura/X11.

Additionally, add a DCHECK to make sure CursorThemeManager is always
initialized in X11 builds.

Bug: 1126830
Change-Id: Ia9e9bbbd9d277df2a432f3cb344d3b30b9551f30
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2401621Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Henrique Ferreiro <hferreiro@igalia.com>
Cr-Commit-Position: refs/heads/master@{#806154}

chrome/browser/ui/views/chrome_browser_main_extra_parts_views_linux.cc

@@ -7,7 +7,6 @@
 #include "chrome/browser/themes/theme_service_aura_linux.h"
 #include "chrome/browser/ui/browser_list.h"
 #include "chrome/browser/ui/views/theme_profile_key.h"
-#include "ui/base/ui_base_features.h"
 #include "ui/display/screen.h"
 #include "ui/views/linux_ui/linux_ui.h"
 
@@ -23,6 +22,7 @@
 #if defined(USE_X11)
 #include "ui/gfx/x/connection.h"  // nogncheck
 #if BUILDFLAG(USE_GTK)
+#include "ui/base/ui_base_features.h"
 #include "ui/gtk/x/gtk_ui_delegate_x11.h"  // nogncheck
 #endif  // BUILDFLAG(USE_GTK)
 #endif  // defined(USE_X11)
@@ -86,10 +86,9 @@ void ChromeBrowserMainExtraPartsViewsLinux::ToolkitInitialized() {
   views::LinuxUI::SetInstance(linux_ui);
   linux_ui->Initialize();
 
-#if defined(USE_OZONE)
-  if (features::IsUsingOzonePlatform())
-    ui::CursorFactory::GetInstance()->ObserveThemeChanges();
-#endif
+  // Cursor theme changes are tracked by LinuxUI (via a CursorThemeManager
+  // implementation). Start observing them once it's initialized.
+  ui::CursorFactory::GetInstance()->ObserveThemeChanges();
 
   DCHECK(ui::LinuxInputMethodContextFactory::instance())
       << "LinuxUI must set LinuxInputMethodContextFactory instance.";

ui/base/x/x11_cursor_factory.cc

@@ -203,8 +203,8 @@ void X11CursorFactory::UnrefImageCursor(PlatformCursor cursor) {
 
 void X11CursorFactory::ObserveThemeChanges() {
   auto* cursor_theme_manager = CursorThemeManager::GetInstance();
-  if (cursor_theme_manager)
-    cursor_theme_observer_.Add(cursor_theme_manager);
+  DCHECK(cursor_theme_manager);
+  cursor_theme_observer_.Add(cursor_theme_manager);
 }
 
 void X11CursorFactory::OnCursorThemeNameChanged(