ozone: xkb: Load keymaps on worker thread & cache them

ui/events/ozone/layout/xkb/xkb_keyboard_layout_engine.h

Index: ui/events/ozone/layout/xkb/xkb_keyboard_layout_engine.h
diff --git a/ui/events/ozone/layout/xkb/xkb_keyboard_layout_engine.h b/ui/events/ozone/layout/xkb/xkb_keyboard_layout_engine.h
index d7a98545d3a435c884854f069798f9b72bcc1b4d..9b7227b15bca848f0e8477950cb7025dd81fc650 100644
--- a/ui/events/ozone/layout/xkb/xkb_keyboard_layout_engine.h
+++ b/ui/events/ozone/layout/xkb/xkb_keyboard_layout_engine.h
@@ -5,9 +5,11 @@
 #ifndef UI_EVENTS_OZONE_LAYOUT_XKB_XKB_KEYBOARD_LAYOUT_ENGINE_H_
 #define UI_EVENTS_OZONE_LAYOUT_XKB_XKB_KEYBOARD_LAYOUT_ENGINE_H_
 
+#include <map>
 #include <xkbcommon/xkbcommon.h>
 
 #include "base/containers/hash_tables.h"
+#include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/strings/string16.h"
 #include "ui/events/ozone/layout/events_ozone_layout_export.h"
@@ -86,6 +88,24 @@ class EVENTS_OZONE_LAYOUT_EXPORT XkbKeyboardLayoutEngine
   // so we need to trigger its cleanup.
   scoped_ptr<xkb_context, XkbContextDeleter> xkb_context_;
   scoped_ptr<xkb_state, XkbStateDeleter> xkb_state_;
+  std::map<std::string, xkb_keymap*> xkb_keymaps_;
+
+  // The class is used to load keymap files.
+  class XkbKeymapLoader : public base::RefCountedThreadSafe<XkbKeymapLoader> {
+   public:
+    explicit XkbKeymapLoader(XkbKeyboardLayoutEngine* layout_engine);
+    void loadKeymap(const std::string& layout_name);
+
+   private:
+     friend class base::RefCountedThreadSafe<XkbKeymapLoader>;
+     ~XkbKeymapLoader() {}
+     XkbKeyboardLayoutEngine* layout_engine_;
+     struct xkb_rule_names* names;
+     // Uses xkb_keymap_new_from_names from libxkbcommon to load keymap file,
+     // And pushes this keymap file load into FILE thread.
+     void startLoadKeymap(const std::string& layout_name,
+                          xkb_rule_names* names);
+  };
 };
 
 }  // namespace ui