Linux: Add support for custom cursor themes

Use the cursor theme that GTK tells us is the default,
instead of always using the default white cursor theme.

BUG=377525

Review-Url: https://codereview.chromium.org/2135353002
Cr-Commit-Position: refs/heads/master@{#405261}

chrome/browser/ui/libgtk2ui/gtk2_ui.cc

@@ -6,6 +6,7 @@
 
 #include <math.h>
 #include <pango/pango.h>
+#include <X11/Xcursor/Xcursor.h>
 #include <set>
 #include <utility>
 
@@ -49,6 +50,7 @@
 #include "ui/gfx/image/image_skia_source.h"
 #include "ui/gfx/skbitmap_operations.h"
 #include "ui/gfx/skia_util.h"
+#include "ui/gfx/x/x11_types.h"
 #include "ui/native_theme/native_theme.h"
 #include "ui/resources/grit/ui_resources.h"
 #include "ui/views/controls/button/blue_button.h"
@@ -508,9 +510,10 @@ void Gtk2UI::Initialize() {
                          G_CALLBACK(OnThemeChanged),
                          this);
 
-
   LoadGtkValues();
 
+  LoadCursorTheme();
+
 #if defined(ENABLE_BASIC_PRINTING)
   printing::PrintingContextLinux::SetCreatePrintDialogFunction(
       &PrintDialogGtk2::CreatePrintDialog);
@@ -996,6 +999,24 @@ void Gtk2UI::LoadGtkValues() {
       theme->GetSystemColor(ui::NativeTheme::kColorId_ThrobberWaitingColor);
 }
 
+void Gtk2UI::LoadCursorTheme() {
+  GtkSettings* settings = gtk_settings_get_default();
+
+  gchar* theme = nullptr;
+  gint size = 0;
+  g_object_get(settings,
+               "gtk-cursor-theme-name", &theme,
+               "gtk-cursor-theme-size", &size,
+               nullptr);
+
+  if (theme)
+    XcursorSetTheme(gfx::GetXDisplay(), theme);
+  if (size)
+    XcursorSetDefaultSize(gfx::GetXDisplay(), size);
+
+  g_free(theme);
+}
+
 void Gtk2UI::UpdateMaterialDesignColors() {
   // TODO(varkha): This should be merged back into LoadGtkValues() once Material
   // Design is on unconditionally.

chrome/browser/ui/libgtk2ui/gtk2_ui.h

@@ -134,6 +134,9 @@ class Gtk2UI : public views::LinuxUI {
   // ThemeService interface and the colors we send to webkit.
   void LoadGtkValues();
 
+  // Initialize the Xcursor theme and size with the GTK theme and size.
+  void LoadCursorTheme();
+
   // Updates colors if necessary after possible modification of command line.
   // TODO(varkha): This should not be necessary once Material Design is on
   // unconditionally.