Split NTPLoginHandler across chrome://apps and chrome://history.

NTPLoginHandler was originally used to handle login from the NTP. It now
handles login on chrome://apps and chrome://history and employs a dirty
little hack to be re-used.

Undo that hack (exposing of ntp.updateLogin on chrome://history) and
split the handler logically, slimming the history handler
(which runs on mobile).

R=mad@chromium.org
BUG=329637

Review URL: https://codereview.chromium.org/1143963002

Cr-Commit-Position: refs/heads/master@{#330874}

chrome/browser/resources/history/other_devices.js

@@ -535,15 +535,10 @@ function setForeignSessions(sessionList, isTabSyncEnabled) {
 }
 
 /**
- * Called when this element is initialized, and from the new tab page when
- * the user's signed in state changes,
- * @param {string} header The first line of text (unused here).
- * @param {string} subHeader The second line of text (unused here).
- * @param {string} iconURL The url for the login status icon. If this is null
- then the login status icon is hidden (unused here).
+ * Called when initialized or the user's signed in state changes,
  * @param {boolean} isUserSignedIn Is the user currently signed in?
  */
-function updateLogin(header, subHeader, iconURL, isUserSignedIn) {
+function updateSignInState(isUserSignedIn) {
   if (devicesView)
     devicesView.updateSignInState(isUserSignedIn);
 }
@@ -557,15 +552,6 @@ function load() {
   if (!loadTimeData.getBoolean('isInstantExtendedApiEnabled'))
     return;
 
-  // We must use this namespace to reuse the handler code for foreign session
-  // and login. TODO(estade): change the call site in ntp_login_handler.cc so
-  // this hack isn't necessary.
-  cr.define('ntp', function() {
-    return {
-      updateLogin: updateLogin
-    };
-  });
-
   devicesView = new DevicesView();
 
   // Create the context menu that appears when the user right clicks
@@ -577,6 +563,8 @@ function load() {
   };
   $('search-field').addEventListener('search', doSearch);
   $('search-button').addEventListener('click', doSearch);
+
+  chrome.send('otherDevicesInitialized');
 }
 
 // Add handlers to HTML elements.

chrome/browser/ui/webui/ntp/ntp_login_handler.cc → chrome/browser/ui/webui/app_launcher_login_handler.cc

@@ -2,14 +2,13 @@
 // 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/ntp/ntp_login_handler.h"
+#include "chrome/browser/ui/webui/app_launcher_login_handler.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/metrics/histogram.h"
-#include "base/prefs/pref_notifier.h"
 #include "base/prefs/pref_service.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/values.h"
@@ -27,6 +26,7 @@
 #include "chrome/browser/ui/browser_window.h"
 #include "chrome/browser/ui/chrome_pages.h"
 #include "chrome/browser/ui/webui/ntp/new_tab_ui.h"
+#include "chrome/browser/ui/webui/profile_info_watcher.h"
 #include "chrome/browser/web_resource/promo_resource_service.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/common/url_constants.h"
@@ -79,52 +79,37 @@ base::string16 CreateElementWithClass(const base::string16& content,
 
 }  // namespace
 
-NTPLoginHandler::NTPLoginHandler() {
-}
-
-NTPLoginHandler::~NTPLoginHandler() {
-  ProfileManager* profile_manager = g_browser_process->profile_manager();
-  // The profile_manager might be NULL in testing environments.
-  if (profile_manager)
-    profile_manager->GetProfileInfoCache().RemoveObserver(this);
-}
+AppLauncherLoginHandler::AppLauncherLoginHandler() {}
 
-void NTPLoginHandler::RegisterMessages() {
-  ProfileManager* profile_manager = g_browser_process->profile_manager();
-  // The profile_manager might be NULL in testing environments.
-  if (profile_manager)
-    profile_manager->GetProfileInfoCache().AddObserver(this);
+AppLauncherLoginHandler::~AppLauncherLoginHandler() {}
 
-  PrefService* pref_service = Profile::FromWebUI(web_ui())->GetPrefs();
-  signin_allowed_pref_.Init(prefs::kSigninAllowed,
-                            pref_service,
-                            base::Bind(&NTPLoginHandler::UpdateLogin,
-                                       base::Unretained(this)));
+void AppLauncherLoginHandler::RegisterMessages() {
+  profile_info_watcher_.reset(new ProfileInfoWatcher(
+      Profile::FromWebUI(web_ui()),
+      base::Bind(&AppLauncherLoginHandler::UpdateLogin,
+                 base::Unretained(this))));
 
   web_ui()->RegisterMessageCallback("initializeSyncLogin",
-      base::Bind(&NTPLoginHandler::HandleInitializeSyncLogin,
+      base::Bind(&AppLauncherLoginHandler::HandleInitializeSyncLogin,
                  base::Unretained(this)));
   web_ui()->RegisterMessageCallback("showSyncLoginUI",
-      base::Bind(&NTPLoginHandler::HandleShowSyncLoginUI,
+      base::Bind(&AppLauncherLoginHandler::HandleShowSyncLoginUI,
                  base::Unretained(this)));
   web_ui()->RegisterMessageCallback("loginMessageSeen",
-      base::Bind(&NTPLoginHandler::HandleLoginMessageSeen,
+      base::Bind(&AppLauncherLoginHandler::HandleLoginMessageSeen,
                  base::Unretained(this)));
   web_ui()->RegisterMessageCallback("showAdvancedLoginUI",
-      base::Bind(&NTPLoginHandler::HandleShowAdvancedLoginUI,
+      base::Bind(&AppLauncherLoginHandler::HandleShowAdvancedLoginUI,
                  base::Unretained(this)));
 }
 
-void NTPLoginHandler::OnProfileAuthInfoChanged(
-    const base::FilePath& profile_path) {
-  UpdateLogin();
-}
-
-void NTPLoginHandler::HandleInitializeSyncLogin(const base::ListValue* args) {
+void AppLauncherLoginHandler::HandleInitializeSyncLogin(
+    const base::ListValue* args) {
   UpdateLogin();
 }
 
-void NTPLoginHandler::HandleShowSyncLoginUI(const base::ListValue* args) {
+void AppLauncherLoginHandler::HandleShowSyncLoginUI(
+    const base::ListValue* args) {
   Profile* profile = Profile::FromWebUI(web_ui());
   if (!signin::ShouldShowPromo(profile))
     return;
@@ -148,7 +133,7 @@ void NTPLoginHandler::HandleShowSyncLoginUI(const base::ListValue* args) {
   RecordInHistogram(NTP_SIGN_IN_PROMO_CLICKED);
 }
 
-void NTPLoginHandler::RecordInHistogram(int type) {
+void AppLauncherLoginHandler::RecordInHistogram(int type) {
   // Invalid type to record.
   if (type < NTP_SIGN_IN_PROMO_VIEWED ||
       type > NTP_SIGN_IN_PROMO_CLICKED) {
@@ -159,7 +144,8 @@ void NTPLoginHandler::RecordInHistogram(int type) {
   }
 }
 
-void NTPLoginHandler::HandleLoginMessageSeen(const base::ListValue* args) {
+void AppLauncherLoginHandler::HandleLoginMessageSeen(
+    const base::ListValue* args) {
   Profile::FromWebUI(web_ui())->GetPrefs()->SetBoolean(
       prefs::kSignInPromoShowNTPBubble, false);
   NewTabUI* ntp_ui = NewTabUI::FromWebUIController(web_ui()->GetController());
@@ -168,26 +154,19 @@ void NTPLoginHandler::HandleLoginMessageSeen(const base::ListValue* args) {
     ntp_ui->set_showing_sync_bubble(true);
 }
 
-void NTPLoginHandler::HandleShowAdvancedLoginUI(const base::ListValue* args) {
+void AppLauncherLoginHandler::HandleShowAdvancedLoginUI(
+    const base::ListValue* args) {
   Browser* browser =
       chrome::FindBrowserWithWebContents(web_ui()->GetWebContents());
   if (browser)
     chrome::ShowBrowserSignin(browser, signin_metrics::SOURCE_NTP_LINK);
 }
 
-void NTPLoginHandler::UpdateLogin() {
-  Profile* profile = Profile::FromWebUI(web_ui());
-  SigninManagerBase* signin_manager =
-      SigninManagerFactory::GetForProfile(profile);
-  if (!signin_manager) {
-    // Guests on desktop do not have a signin manager.
-    return;
-  }
-
-  std::string username = signin_manager->GetAuthenticatedUsername();
-
+void AppLauncherLoginHandler::UpdateLogin() {
+  std::string username = profile_info_watcher_->GetAuthenticatedUsername();
   base::string16 header, sub_header;
   std::string icon_url;
+  Profile* profile = Profile::FromWebUI(web_ui());
   if (!username.empty()) {
     ProfileInfoCache& cache =
         g_browser_process->profile_manager()->GetProfileInfoCache();
@@ -240,7 +219,7 @@ void NTPLoginHandler::UpdateLogin() {
 }
 
 // static
-bool NTPLoginHandler::ShouldShow(Profile* profile) {
+bool AppLauncherLoginHandler::ShouldShow(Profile* profile) {
 #if defined(OS_CHROMEOS)
   // For now we don't care about showing sync status on Chrome OS. The promo
   // UI and the avatar menu don't exist on that platform.
@@ -252,8 +231,8 @@ bool NTPLoginHandler::ShouldShow(Profile* profile) {
 }
 
 // static
-void NTPLoginHandler::GetLocalizedValues(Profile* profile,
-                                         base::DictionaryValue* values) {
+void AppLauncherLoginHandler::GetLocalizedValues(
+    Profile* profile, base::DictionaryValue* values) {
   PrefService* prefs = profile->GetPrefs();
   bool hide_sync = !prefs->GetBoolean(prefs::kSignInPromoShowNTPBubble);
 

chrome/browser/ui/webui/ntp/ntp_login_handler.h → chrome/browser/ui/webui/app_launcher_login_handler.h

@@ -2,30 +2,27 @@
 // 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_NTP_NTP_LOGIN_HANDLER_H_
-#define CHROME_BROWSER_UI_WEBUI_NTP_NTP_LOGIN_HANDLER_H_
+#ifndef CHROME_BROWSER_UI_WEBUI_APP_LAUNCHER_LOGIN_HANDLER_H_
+#define CHROME_BROWSER_UI_WEBUI_APP_LAUNCHER_LOGIN_HANDLER_H_
 
-#include "base/prefs/pref_member.h"
-#include "chrome/browser/profiles/profile_info_cache_observer.h"
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
 #include "content/public/browser/web_ui_message_handler.h"
 
 class Profile;
+class ProfileInfoWatcher;
 
-// The NTP login handler currently simply displays the current logged in
+// The login handler currently simply displays the current logged in
 // username at the top of the NTP (and update itself when that changes).
 // In the future it may expand to allow users to login from the NTP.
-class NTPLoginHandler : public content::WebUIMessageHandler,
-                        public ProfileInfoCacheObserver {
+class AppLauncherLoginHandler : public content::WebUIMessageHandler {
  public:
-  NTPLoginHandler();
-  ~NTPLoginHandler() override;
+  AppLauncherLoginHandler();
+  ~AppLauncherLoginHandler() override;
 
   // WebUIMessageHandler implementation:
   void RegisterMessages() override;
 
-  // ProfileInfoCacheObserver implementation:
-  void OnProfileAuthInfoChanged(const base::FilePath& profile_path) override;
-
   // Returns true if the login handler should be shown in a new tab page
   // for the given |profile|. |profile| must not be NULL.
   static bool ShouldShow(Profile* profile);
@@ -66,7 +63,11 @@ class NTPLoginHandler : public content::WebUIMessageHandler,
   // Internal helper method
   void UpdateLogin();
 
-  BooleanPrefMember signin_allowed_pref_;
+  // Watches this web UI's profile for info changes (e.g. authenticated username
+  // changes).
+  scoped_ptr<ProfileInfoWatcher> profile_info_watcher_;
+
+  DISALLOW_COPY_AND_ASSIGN(AppLauncherLoginHandler);
 };
 
-#endif  // CHROME_BROWSER_UI_WEBUI_NTP_NTP_LOGIN_HANDLER_H_
+#endif  // CHROME_BROWSER_UI_WEBUI_APP_LAUNCHER_LOGIN_HANDLER_H_

chrome/browser/ui/webui/app_launcher_page_ui.cc

@@ -7,12 +7,12 @@
 #include "base/memory/ref_counted_memory.h"
 #include "base/metrics/histogram.h"
 #include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/ui/webui/app_launcher_login_handler.h"
 #include "chrome/browser/ui/webui/metrics_handler.h"
 #include "chrome/browser/ui/webui/ntp/app_launcher_handler.h"
 #include "chrome/browser/ui/webui/ntp/app_resource_cache_factory.h"
 #include "chrome/browser/ui/webui/ntp/core_app_launcher_handler.h"
 #include "chrome/browser/ui/webui/ntp/favicon_webui_handler.h"
-#include "chrome/browser/ui/webui/ntp/ntp_login_handler.h"
 #include "chrome/browser/ui/webui/ntp/ntp_resource_cache.h"
 #include "chrome/common/url_constants.h"
 #include "chrome/grit/generated_resources.h"
@@ -39,8 +39,8 @@ AppLauncherPageUI::AppLauncherPageUI(content::WebUI* web_ui)
     : content::WebUIController(web_ui) {
   web_ui->OverrideTitle(l10n_util::GetStringUTF16(IDS_APP_LAUNCHER_TAB_TITLE));
 
-  if (NTPLoginHandler::ShouldShow(GetProfile()))
-    web_ui->AddMessageHandler(new NTPLoginHandler());
+  if (AppLauncherLoginHandler::ShouldShow(GetProfile()))
+    web_ui->AddMessageHandler(new AppLauncherLoginHandler());
 
   if (!GetProfile()->IsOffTheRecord()) {
     ExtensionService* service =

chrome/browser/ui/webui/history_login_handler.cc

+// Copyright 2015 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/history_login_handler.h"
+
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/values.h"
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/ui/webui/profile_info_watcher.h"
+#include "content/public/browser/web_ui.h"
+
+HistoryLoginHandler::HistoryLoginHandler() {}
+HistoryLoginHandler::~HistoryLoginHandler() {}
+
+void HistoryLoginHandler::RegisterMessages() {
+  profile_info_watcher_.reset(new ProfileInfoWatcher(
+      Profile::FromWebUI(web_ui()),
+      base::Bind(&HistoryLoginHandler::ProfileInfoChanged,
+                 base::Unretained(this))));
+
+  web_ui()->RegisterMessageCallback("otherDevicesInitialized",
+      base::Bind(&HistoryLoginHandler::HandleOtherDevicesInitialized,
+                 base::Unretained(this)));
+}
+
+void HistoryLoginHandler::HandleOtherDevicesInitialized(
+    const base::ListValue* /*args*/) {
+  ProfileInfoChanged();
+}
+
+void HistoryLoginHandler::ProfileInfoChanged() {
+  bool signed_in = !profile_info_watcher_->GetAuthenticatedUsername().empty();
+  web_ui()->CallJavascriptFunction(
+      "updateSignInState", base::FundamentalValue(signed_in));
+}

chrome/browser/ui/webui/history_login_handler.h

+// Copyright 2015 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_HISTORY_LOGIN_HANDLER_H_
+#define CHROME_BROWSER_UI_WEBUI_HISTORY_LOGIN_HANDLER_H_
+
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "content/public/browser/web_ui_message_handler.h"
+
+class ProfileInfoWatcher;
+
+// The handler for login-related messages from chrome://history.
+class HistoryLoginHandler : public content::WebUIMessageHandler {
+ public:
+  HistoryLoginHandler();
+  ~HistoryLoginHandler() override;
+
+  // WebUIMessageHandler implementation.
+  void RegisterMessages() override;
+
+ private:
+  // Handler for the "otherDevicesInitialized" message. No args.
+  void HandleOtherDevicesInitialized(const base::ListValue* args);
+
+  // Called by |profile_info_watcher_| on desktop if profile info changes.
+  void ProfileInfoChanged();
+
+  // Watches this web UI's profile for info changes (e.g. authenticated username
+  // changes).
+  scoped_ptr<ProfileInfoWatcher> profile_info_watcher_;
+
+  DISALLOW_COPY_AND_ASSIGN(HistoryLoginHandler);
+};
+
+#endif  // CHROME_BROWSER_UI_WEBUI_HISTORY_LOGIN_HANDLER_H_

chrome/browser/ui/webui/history_ui.cc

@@ -75,7 +75,7 @@
 
 #if !defined(OS_ANDROID) && !defined(OS_IOS)
 #include "chrome/browser/ui/webui/foreign_session_handler.h"
-#include "chrome/browser/ui/webui/ntp/ntp_login_handler.h"
+#include "chrome/browser/ui/webui/history_login_handler.h"
 #endif
 
 using bookmarks::BookmarkModel;
@@ -1029,11 +1029,11 @@ HistoryUI::HistoryUI(content::WebUI* web_ui) : WebUIController(web_ui) {
   web_ui->AddMessageHandler(new BrowsingHistoryHandler());
   web_ui->AddMessageHandler(new MetricsHandler());
 
-// On mobile we deal with foreign sessions differently.
+  // On mobile we deal with foreign sessions differently.
 #if !defined(OS_ANDROID) && !defined(OS_IOS)
   if (chrome::IsInstantExtendedAPIEnabled()) {
     web_ui->AddMessageHandler(new browser_sync::ForeignSessionHandler());
-    web_ui->AddMessageHandler(new NTPLoginHandler());
+    web_ui->AddMessageHandler(new HistoryLoginHandler());
   }
 #endif
 
@@ -1042,6 +1042,8 @@ HistoryUI::HistoryUI(content::WebUI* web_ui) : WebUIController(web_ui) {
   content::WebUIDataSource::Add(profile, CreateHistoryUIHTMLSource(profile));
 }
 
+HistoryUI::~HistoryUI() {}
+
 // static
 base::RefCountedMemory* HistoryUI::GetFaviconResourceBytes(
       ui::ScaleFactor scale_factor) {

chrome/browser/ui/webui/history_ui.h

@@ -7,6 +7,7 @@
 
 #include <string>
 
+#include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/scoped_observer.h"
 #include "base/strings/string16.h"
@@ -219,6 +220,7 @@ class BrowsingHistoryHandler : public content::WebUIMessageHandler,
 class HistoryUI : public content::WebUIController {
  public:
   explicit HistoryUI(content::WebUI* web_ui);
+  ~HistoryUI() override;
 
   static base::RefCountedMemory* GetFaviconResourceBytes(
       ui::ScaleFactor scale_factor);

chrome/browser/ui/webui/ntp/new_tab_ui.cc

@@ -20,7 +20,6 @@
 #include "chrome/browser/ui/webui/ntp/favicon_webui_handler.h"
 #include "chrome/browser/ui/webui/ntp/new_tab_page_handler.h"
 #include "chrome/browser/ui/webui/ntp/new_tab_page_sync_handler.h"
-#include "chrome/browser/ui/webui/ntp/ntp_login_handler.h"
 #include "chrome/browser/ui/webui/ntp/ntp_resource_cache.h"
 #include "chrome/browser/ui/webui/ntp/ntp_resource_cache_factory.h"
 #include "chrome/browser/ui/webui/ntp/ntp_user_data_logger.h"
@@ -105,9 +104,6 @@ NewTabUI::NewTabUI(content::WebUI* web_ui)
       web_ui->AddMessageHandler(new AppLauncherHandler(service));
   }
 
-  if (NTPLoginHandler::ShouldShow(profile))
-    web_ui->AddMessageHandler(new NTPLoginHandler());
-
 #if defined(ENABLE_THEMES)
   // The theme handler can require some CPU, so do it after hooking up the most
   // visited handler. This allows the DB query for the new tab thumbs to happen

chrome/browser/ui/webui/ntp/ntp_resource_cache.cc

@@ -31,9 +31,9 @@
 #include "chrome/browser/ui/apps/app_info_dialog.h"
 #include "chrome/browser/ui/bookmarks/bookmark_bar_constants.h"
 #include "chrome/browser/ui/sync/sync_promo_ui.h"
+#include "chrome/browser/ui/webui/app_launcher_login_handler.h"
 #include "chrome/browser/ui/webui/ntp/new_tab_page_handler.h"
 #include "chrome/browser/ui/webui/ntp/new_tab_ui.h"
-#include "chrome/browser/ui/webui/ntp/ntp_login_handler.h"
 #include "chrome/browser/web_resource/notification_promo.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/pref_names.h"
@@ -448,7 +448,7 @@ void NTPResourceCache::CreateNewTabHTML() {
   load_time_data.SetString("syncLinkText",
       l10n_util::GetStringUTF16(IDS_SYNC_ADVANCED_OPTIONS));
   load_time_data.SetBoolean("shouldShowSyncLogin",
-                            NTPLoginHandler::ShouldShow(profile_));
+                            AppLauncherLoginHandler::ShouldShow(profile_));
   load_time_data.SetString("learnMore",
       l10n_util::GetStringUTF16(IDS_LEARN_MORE));
   const std::string& app_locale = g_browser_process->GetApplicationLocale();
@@ -489,7 +489,7 @@ void NTPResourceCache::CreateNewTabHTML() {
 #endif
 
   NewTabPageHandler::GetLocalizedValues(profile_, &load_time_data);
-  NTPLoginHandler::GetLocalizedValues(profile_, &load_time_data);
+  AppLauncherLoginHandler::GetLocalizedValues(profile_, &load_time_data);
 
   webui::SetLoadTimeDataDefaults(app_locale, &load_time_data);
 

chrome/browser/ui/webui/profile_info_watcher.cc

+// Copyright 2015 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/profile_info_watcher.h"
+
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/prefs/pref_service.h"
+#include "chrome/browser/browser_process.h"
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/profiles/profile_info_cache.h"
+#include "chrome/browser/profiles/profile_manager.h"
+#include "chrome/browser/signin/signin_manager_factory.h"
+#include "chrome/common/pref_names.h"
+#include "components/signin/core/browser/signin_manager.h"
+
+ProfileInfoWatcher::ProfileInfoWatcher(
+    Profile* profile, const base::Closure& callback)
+    : profile_(profile), callback_(callback) {
+  DCHECK(profile_);
+  DCHECK(!callback_.is_null());
+
+  ProfileManager* profile_manager = g_browser_process->profile_manager();
+  // The profile_manager might be NULL in testing environments.
+  if (profile_manager)
+    profile_manager->GetProfileInfoCache().AddObserver(this);
+
+  signin_allowed_pref_.Init(prefs::kSigninAllowed, profile_->GetPrefs(),
+      base::Bind(&ProfileInfoWatcher::RunCallback, base::Unretained(this)));
+}
+
+ProfileInfoWatcher::~ProfileInfoWatcher() {
+  ProfileManager* profile_manager = g_browser_process->profile_manager();
+  // The profile_manager might be NULL in testing environments.
+  if (profile_manager)
+    profile_manager->GetProfileInfoCache().RemoveObserver(this);
+}
+
+void ProfileInfoWatcher::OnProfileAuthInfoChanged(
+    const base::FilePath& profile_path) {
+  RunCallback();
+}
+
+std::string ProfileInfoWatcher::GetAuthenticatedUsername() const {
+  std::string username;
+  SigninManagerBase* signin_manager = GetSigninManager();
+  if (signin_manager)
+    username = signin_manager->GetAuthenticatedUsername();
+  return username;
+}
+
+SigninManagerBase* ProfileInfoWatcher::GetSigninManager() const {
+  return SigninManagerFactory::GetForProfile(profile_);
+}
+
+void ProfileInfoWatcher::RunCallback() {
+  if (GetSigninManager())
+    callback_.Run();
+}

chrome/browser/ui/webui/profile_info_watcher.h

+// Copyright 2015 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_PROFILE_INFO_WATCHER_H_
+#define CHROME_BROWSER_UI_WEBUI_PROFILE_INFO_WATCHER_H_
+
+#include <string>
+
+#include "base/callback.h"
+#include "base/macros.h"
+#include "base/prefs/pref_member.h"
+#include "chrome/browser/profiles/profile_info_cache_observer.h"
+
+class Profile;
+class SigninManagerBase;
+
+// Watches profiles for changes in their cached info (e.g. the authenticated
+// username changes).
+class ProfileInfoWatcher : public ProfileInfoCacheObserver {
+ public:
+  ProfileInfoWatcher(Profile* profile, const base::Closure& callback);
+  ~ProfileInfoWatcher() override;
+
+  // Gets the authenticated username (e.g. username@gmail.com) for |profile_|.
+  std::string GetAuthenticatedUsername() const;
+
+ private:
+  // ProfileInfoCacheObserver:
+  void OnProfileAuthInfoChanged(const base::FilePath& profile_path) override;
+
+  // Gets the SigninManagerBase for |profile_|.
+  SigninManagerBase* GetSigninManager() const;
+
+  // Runs |callback_| when a profile changes. No-ops if |GetSigninManager()|
+  // returns nullptr.
+  void RunCallback();
+
+  // Weak reference to the profile this class observes.
+  Profile* const profile_;
+
+  // Called when the authenticated username changes.
+  base::Closure callback_;
+
+  BooleanPrefMember signin_allowed_pref_;
+
+  DISALLOW_COPY_AND_ASSIGN(ProfileInfoWatcher);
+};
+
+#endif  // CHROME_BROWSER_UI_WEBUI_PROFILE_INFO_WATCHER_H_

chrome/chrome_browser_ui.gypi

@@ -1733,6 +1733,8 @@
       'browser/ui/website_settings/permission_menu_model.h',
       'browser/ui/website_settings/website_settings_utils.cc',
       'browser/ui/website_settings/website_settings_utils.h',
+      'browser/ui/webui/app_launcher_login_handler.cc',
+      'browser/ui/webui/app_launcher_login_handler.h',
       'browser/ui/webui/bookmarks_ui.cc',
       'browser/ui/webui/bookmarks_ui.h',
       'browser/ui/webui/chrome_web_contents_handler.cc',
@@ -1769,6 +1771,8 @@
       'browser/ui/webui/help/version_updater_mac.h',
       'browser/ui/webui/help/version_updater_mac.mm',
       'browser/ui/webui/help/version_updater_win.cc',
+      'browser/ui/webui/history_login_handler.cc',
+      'browser/ui/webui/history_login_handler.h',
       'browser/ui/webui/identity_internals_ui.cc',
       'browser/ui/webui/identity_internals_ui.h',
       'browser/ui/webui/inspect_ui.cc',
@@ -1787,8 +1791,6 @@
       'browser/ui/webui/ntp/new_tab_page_sync_handler.h',
       'browser/ui/webui/ntp/new_tab_ui.cc',
       'browser/ui/webui/ntp/new_tab_ui.h',
-      'browser/ui/webui/ntp/ntp_login_handler.cc',
-      'browser/ui/webui/ntp/ntp_login_handler.h',
       'browser/ui/webui/ntp/ntp_resource_cache.cc',
       'browser/ui/webui/ntp/ntp_resource_cache.h',
       'browser/ui/webui/ntp/ntp_resource_cache_factory.cc',
@@ -1900,6 +1902,8 @@
       'browser/ui/webui/options/website_settings_handler.h',
       'browser/ui/webui/plugins_ui.cc',
       'browser/ui/webui/plugins_ui.h',
+      'browser/ui/webui/profile_info_watcher.cc',
+      'browser/ui/webui/profile_info_watcher.h',
       'browser/ui/webui/quota_internals/quota_internals_handler.cc',
       'browser/ui/webui/quota_internals/quota_internals_handler.h',
       'browser/ui/webui/quota_internals/quota_internals_proxy.cc',