Adding JS and C++ handlers for events on new Welcome page.

chrome/browser/ui/webui/welcome_handler.cc

+// 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.
+
+#include "chrome/browser/ui/webui/welcome_handler.h"
+
+#include "chrome/browser/signin/profile_oauth2_token_service_factory.h"
+#include "chrome/browser/signin/signin_manager_factory.h"
+#include "chrome/browser/ui/browser_finder.h"
+#include "chrome/browser/ui/browser_navigator.h"
+#include "chrome/browser/ui/profile_chooser_constants.h"
+#include "chrome/common/url_constants.h"
+#include "components/signin/core/browser/signin_manager.h"
+#include "components/signin/core/browser/signin_metrics.h"
+#include "ui/base/page_transition_types.h"
+
+WelcomeHandler::WelcomeHandler(content::WebUI* web_ui)
+    : profile_(Profile::FromWebUI(web_ui)),
+      browser_(chrome::FindBrowserWithWebContents(web_ui->GetWebContents())),
+      oauth2_token_service_(
+          ProfileOAuth2TokenServiceFactory::GetForProfile(profile_)),
+      result_(WelcomeResult::DEFAULT) {
+  oauth2_token_service_->AddObserver(this);

[michaelpg, 2016/09/23 18:46:35]

According to its comments, this service will be nullptr in incognito mode.
Should we prevent this UI from opening in incognito contexts (similar to how
chrome://settings in an Incognito window opens it in a new on-the-record tab)?

What about Guest mode? (top-right profile icon => switch person => browse as
guest)

[tmartino, 2016/09/26 23:10:15]

Done. Added an early exit to welcome_ui.cc constructor. The result is simply
showing a "This page can't be reached" page.

+}
+
+WelcomeHandler::~WelcomeHandler() {
+  oauth2_token_service_->RemoveObserver(this);
+  // TODO(tmartino): Log to UMA according to WelcomeResult.
+}
+
+// Override from OAuth2TokenService::Observer. Occurs when a new auth token is
+// available.
+void WelcomeHandler::OnRefreshTokenAvailable(const std::string& account_id) {
+  result_ = WelcomeResult::SIGNED_IN;
+  GoToNewTabPage();
+}
+
+// Handles backend events necessary when user clicks "Sign in."
+void WelcomeHandler::HandleActivateSignIn(const base::ListValue* args) {
+  if (SigninManagerFactory::GetForProfile(profile_)->IsAuthenticated()) {
+    // In general, this page isn't shown to signed-in users; however, if one
+    // should arrive here, then opening the sign-in dialog will likely lead
+    // to a crash. Thus, we just act like sign-in was "successful" and whisk
+    // them away to the NTP instead.
+    GoToNewTabPage();
+  } else {
+    browser_->ShowModalSigninWindow(
+        profiles::BubbleViewMode::BUBBLE_VIEW_MODE_GAIA_SIGNIN,
+        signin_metrics::AccessPoint::ACCESS_POINT_START_PAGE);
+  }
+}
+
+// Handles backend events necessary when user clicks "No thanks."
+void WelcomeHandler::HandleUserDecline(const base::ListValue* args) {
+  result_ = WelcomeResult::DECLINED;
+  GoToNewTabPage();
+}
+
+// Override from WebUIMessageHandler.
+void WelcomeHandler::RegisterMessages() {
+  web_ui()->RegisterMessageCallback(
+      "handleActivateSignIn", base::Bind(&WelcomeHandler::HandleActivateSignIn,
+                                         base::Unretained(this)));
+  web_ui()->RegisterMessageCallback(
+      "handleUserDecline",
+      base::Bind(&WelcomeHandler::HandleUserDecline, base::Unretained(this)));
+}
+
+void WelcomeHandler::GoToNewTabPage() {
+  chrome::NavigateParams params(browser_, GURL(chrome::kChromeUINewTabURL),
+                                ui::PageTransition::PAGE_TRANSITION_LINK);
+  chrome::Navigate(&params);
+}