cros: Use runtime stylus detection for ash palette.

chrome/browser/ui/webui/settings/chromeos/device_stylus_handler.h

 // Copyright 2017 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.
 
 #ifndef CHROME_BROWSER_UI_WEBUI_SETTINGS_CHROMEOS_DEVICE_STYLUS_HANDLER_H_
 #define CHROME_BROWSER_UI_WEBUI_SETTINGS_CHROMEOS_DEVICE_STYLUS_HANDLER_H_
 
 #include <set>
 
 #include "base/macros.h"
 #include "chrome/browser/chromeos/note_taking_helper.h"
 #include "chrome/browser/ui/webui/settings/settings_page_ui_handler.h"
+#include "ui/events/devices/input_device_event_observer.h"
+
+namespace base {
+class ListValue;
+}
 
 namespace chromeos {
 namespace settings {
 
+// Chrome OS stylus settings handler.
 class StylusHandler : public ::settings::SettingsPageUIHandler,
-                      public chromeos::NoteTakingHelper::Observer {
+                      public chromeos::NoteTakingHelper::Observer,
+                      public ui::InputDeviceEventObserver {
  public:
   StylusHandler();
   ~StylusHandler() override;
 
   // SettingsPageUIHandler implementation.
   void RegisterMessages() override;
   void OnJavascriptAllowed() override {}
   void OnJavascriptDisallowed() override {}
 
   // chromeos::NoteTakingHelper::Observer implementation.
   void OnAvailableNoteTakingAppsUpdated() override;
 
+  // ui::InputDeviceObserver:
+  void OnDeviceListsComplete() override;
+
  private:
   void UpdateNoteTakingApps();
   void RequestApps(const base::ListValue* unused_args);
   void SetPreferredNoteTakingApp(const base::ListValue* args);
 
+  // Called by JS to request a |SendHasStylus| call.
+  void HandleInitialize(const base::ListValue* args);
+  // Enables or disables the stylus UI section.
+  void SendHasStylus();
+
   // IDs of available note-taking apps.
   std::set<std::string> note_taking_app_ids_;
 
   DISALLOW_COPY_AND_ASSIGN(StylusHandler);
 };
 
 }  // namespace settings
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_UI_WEBUI_SETTINGS_CHROMEOS_DEVICE_STYLUS_HANDLER_H_