Determine the Win10-specific Welcome page variant to display

chrome/browser/ui/webui/welcome_win10_handler.h

 // Copyright 2016 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_WELCOME_WIN10_HANDLER_H_
 #define CHROME_BROWSER_UI_WEBUI_WELCOME_WIN10_HANDLER_H_
 
+#include <memory>
+#include <string>
+
 #include "base/macros.h"
+#include "base/optional.h"
+#include "base/timer/timer.h"
+#include "chrome/common/shell_handler_win.mojom.h"
+#include "content/public/browser/utility_process_mojo_client.h"
 #include "content/public/browser/web_ui_message_handler.h"
 
 namespace base {
 class ListValue;
 }
 
 // Handles actions on the Windows 10 specific Welcome page.
 class WelcomeWin10Handler : public content::WebUIMessageHandler {
  public:
   WelcomeWin10Handler();
   ~WelcomeWin10Handler() override;
 
   // content::WebUIMessageHandler:
   void RegisterMessages() override;
 
  private:
+  // Handlers for javascript calls.
+  void HandleGetPinnedToTaskbarState(const base::ListValue* args);
   void HandleSetDefaultBrowser(const base::ListValue* args);
   void HandleContinue(const base::ListValue* args);
 
+  void StartIsPinnedToTaskbarCheck();
+
+  // Callback for mojom::ShellHandler's call to IsPinnedToTaskbar().
+  void OnIsPinnedToTaskbarResult(bool succeeded, bool is_pinned_to_taskbar);
+
+  // Sets the internal result and optionally call
+  // SendPinnedToTaskbarStateResult() in the case that
+  // |pinned_state_callback_id_| is not empty.
+  void OnIsPinnedToTaskbarDetermined(bool is_pinned_to_taskbar);
+
+  // Returns the result to the getPinnedToTaskbarState() javascript call via the
+  // promise.
+  void SendPinnedToTaskbarStateResult();
+
+  std::unique_ptr<content::UtilityProcessMojoClient<mojom::ShellHandler>>
+      client_;
+  base::OneShotTimer timer_;
+
+  // Acts as a cache to hold the taskbar pinned state of Chrome. It has no value
+  // until this state is determined.
+  base::Optional<bool> pinned_state_result_;

[tmartino, 2016/10/28 21:44:15]

Any meaningful race conditions between the JS handler and the callback kicked
off in the ctor?

[Patrick Monette, 2016/10/29 00:59:12]

It's all happening on the same thread. I added dchecks for it.

+
+  // The callback id used to return the result to the getPinnedToTaskbarState()
+  // javascript call. This id is empty until we receive the call; thus this
+  // variable is used to determine if the result should be sent to the caller
+  // when it is received, or wait for the call to happen.
+  std::string pinned_state_callback_id_;
+
   DISALLOW_COPY_AND_ASSIGN(WelcomeWin10Handler);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_WELCOME_WIN10_HANDLER_H_