Fine tuned availability of hotword plugin.

This CL adds several changes:
- enables the JS handler to turn on and off the hotword recognizer
- adds a pref 'hotword.app_list_enabled' to customize the plugin usage
- synchronization logic, so if the user explicitly turns off
  hotword.search_enabled, hotword.app_list_enabled goes off too
- extract the language check of HotwordService as a static method
  and let StartPageHandler check it, because our hotword
  "Ok, Google" is US-English only

BUG=341710, 341779
R=xiyuan@chromium.org, rlp@chromium.org, estade@chromium.org
TBR=samarth@chromium.org
TEST=manually

Review URL: https://codereview.chromium.org/158143002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251142 0039d316-1c4b-4281-b951-d872f2087c98

19 files changed, 276 insertions, 98 deletions

diff --git a/chrome/app/chromeos_strings.grdp b/chrome/app/chromeos_strings.grdp
index 33c5423..dc076e9 100644
--- a/chrome/app/chromeos_strings.grdp
+++ b/chrome/app/chromeos_strings.grdp
@@ -2451,6 +2451,9 @@ Press any key to continue exploring.
   <message name="IDS_OPTIONS_ENABLE_CONTENT_PROTECTION_ATTESTATION" desc="description label for verified access about premium contents">
     Enable Verified Access
   </message>
+  <message name="IDS_OPTIONS_ENABLE_HOTWORD_APP_LIST" desc="description label for the checkbox to enable/disable hotword in the app list search">
+    Enable "Ok, Google" to start a voice search in the app launcher.
+  </message>
   <message name="IDS_NETWORK_RECONNECT_TITLE" desc="In network menu, title of the reconnect button that allows user to retry connection on error.">
     Reconnect
   </message>
diff --git a/chrome/browser/profiles/chrome_browser_main_extra_parts_profiles.cc b/chrome/browser/profiles/chrome_browser_main_extra_parts_profiles.cc
index 4f35567..c62bef0 100644
--- a/chrome/browser/profiles/chrome_browser_main_extra_parts_profiles.cc
+++ b/chrome/browser/profiles/chrome_browser_main_extra_parts_profiles.cc
@@ -166,6 +166,10 @@
 #include "chrome/browser/profile_resetter/automatic_profile_resetter_factory.h"
 #endif
 
+#if defined(ENABLE_APP_LIST)
+#include "chrome/browser/ui/app_list/start_page_service_factory.h"
+#endif
+
 #if defined(ENABLE_SPELLCHECK)
 #include "chrome/browser/extensions/api/spellcheck/spellcheck_api.h"
 #include "chrome/browser/spellchecker/spellcheck_factory.h"
@@ -203,6 +207,9 @@ ChromeBrowserMainExtraPartsProfiles::~ChromeBrowserMainExtraPartsProfiles() {
 void ChromeBrowserMainExtraPartsProfiles::
 EnsureBrowserContextKeyedServiceFactoriesBuilt() {
   AboutSigninInternalsFactory::GetInstance();
+#if defined(ENABLE_APP_LIST)
+  app_list::StartPageServiceFactory::GetInstance();
+#endif
   autofill::PersonalDataManagerFactory::GetInstance();
 #if !defined(OS_ANDROID)
   AutomaticProfileResetterFactory::GetInstance();
diff --git a/chrome/browser/resources/app_list/speech_manager.js b/chrome/browser/resources/app_list/speech_manager.js
index d58a53f..ebb3afe 100644
--- a/chrome/browser/resources/app_list/speech_manager.js
+++ b/chrome/browser/resources/app_list/speech_manager.js
@@ -127,8 +127,8 @@ cr.define('speech', function() {
       this.setState_(SpeechState.HOTWORD_RECOGNIZING);
     } else {
       this.audioManager_.stop();
+      this.setState_(SpeechState.READY);
     }
-    chrome.send('setSpeechRecognitionState', ['off']);
   };
 
   /**
@@ -158,19 +158,30 @@ cr.define('speech', function() {
   };
 
   /**
-   * Initialize the hotword plugin manager, or do nothing if already
-   * initialization is on.
-   */
-  SpeechManager.prototype.maybeInitializePlugin = function() {
-    if ($('recognizer'))
-      return;
-
-    var pluginManager = new speech.PluginManager(
-        this.onHotwordRecognizerReady_.bind(this),
-        this.onHotwordRecognized_.bind(this));
-    pluginManager.scheduleInitialize(
-        this.audioManager_.getSampleRate(),
-        'chrome://app-list/okgoogle_hotword.config');
+   * Changes the availability of the hotword plugin.
+   *
+   * @param {boolean} enabled Whether enabled or not.
+   */
+  SpeechManager.prototype.setHotwordEnabled = function(enabled) {
+    var recognizer = $('recognizer');
+    if (enabled) {
+      if (recognizer)
+        return;
+
+      var pluginManager = new speech.PluginManager(
+          this.onHotwordRecognizerReady_.bind(this),
+          this.onHotwordRecognized_.bind(this));
+      pluginManager.scheduleInitialize(
+          this.audioManager_.getSampleRate(),
+          'chrome://app-list/okgoogle_hotword.config');
+    } else {
+      if (!recognizer)
+        return;
+      document.body.removeChild(recognizer);
+      this.pluginManager_ = null;
+      if (this.state == SpeechState.HOTWORD_RECOGNIZING)
+        this.setState(SpeechState.READY);
+    }
   };
 
   /**
diff --git a/chrome/browser/resources/app_list/start_page.js b/chrome/browser/resources/app_list/start_page.js
index cc7953c..e1f586e 100644
--- a/chrome/browser/resources/app_list/start_page.js
+++ b/chrome/browser/resources/app_list/start_page.js
@@ -67,10 +67,12 @@ cr.define('appList.startPage', function() {
   }
 
   /**
-   * Invoked when the hotword plugin should be loaded.
+   * Invoked when the hotword plugin availability is changed.
+   *
+   * @param {boolean} enabled Whether the plugin is enabled or not.
    */
-  function maybeInitializePlugin() {
-    speechManager.maybeInitializePlugin();
+  function setHotwordEnabled(enabled) {
+    speechManager.setHotwordEnabled(enabled);
   }
 
   /**
@@ -98,7 +100,7 @@ cr.define('appList.startPage', function() {
   return {
     initialize: initialize,
     setRecommendedApps: setRecommendedApps,
-    maybeInitializePlugin: maybeInitializePlugin,
+    setHotwordEnabled: setHotwordEnabled,
     onAppListShown: onAppListShown,
     onAppListHidden: onAppListHidden,
     toggleSpeechRecognition: toggleSpeechRecognition
diff --git a/chrome/browser/resources/options/browser_options.html b/chrome/browser/resources/options/browser_options.html
index 076c39e..036876a 100644
--- a/chrome/browser/resources/options/browser_options.html
+++ b/chrome/browser/resources/options/browser_options.html
@@ -352,8 +352,14 @@
           </span>
         </span>
       </div>
+      <div id="hotword-app-list" class="checkbox" hidden>
+        <label>
+          <input pref="hotword.app_list_enabled" type="checkbox">
+          <span i18n-content="enableHotwordAppList"></span>
+        </label>
+      </div>
 </if>
-      <div id ="hotword-search" hidden>
+      <div id="hotword-search" hidden>
         <div class="checkbox">
           <span class="controlled-setting-with-label">
             <input id="hotword-search-enable" pref="hotword.search_enabled"
diff --git a/chrome/browser/resources/options/browser_options.js b/chrome/browser/resources/options/browser_options.js
index cc01414..dfa6bc8 100644
--- a/chrome/browser/resources/options/browser_options.js
+++ b/chrome/browser/resources/options/browser_options.js
@@ -230,6 +230,8 @@ cr.define('options', function() {
           chrome.send('coreOptionsUserMetricsAction',
               ['Options_ManageAccounts']);
         };
+        $('hotword-app-list').hidden =
+            !loadTimeData.getBoolean('shouldShowAppListHotword');
       } else {
         $('import-data').onclick = function(event) {
           ImportDataOverlay.show();
diff --git a/chrome/browser/search/hotword_service.cc b/chrome/browser/search/hotword_service.cc
index 713f9f8..544974f 100644
--- a/chrome/browser/search/hotword_service.cc
+++ b/chrome/browser/search/hotword_service.cc
@@ -26,6 +26,21 @@ const char kHotwordFieldTrialName[] = "VoiceTrigger";
 const char kHotwordFieldTrialDisabledGroupName[] = "Disabled";
 }  // namespace hotword_internal
 
+// static
+bool HotwordService::DoesHotwordSupportLanguage(Profile* profile) {
+  std::string locale =
+#if defined(OS_CHROMEOS)
+      // On ChromeOS locale is per-profile.
+      profile->GetPrefs()->GetString(prefs::kApplicationLocale);
+#else
+      g_browser_process->GetApplicationLocale();
+#endif
+  // Only available for English now.
+  std::string normalized_locale = l10n_util::NormalizeLocale(locale);
+  return normalized_locale == "en" || normalized_locale == "en_us" ||
+      normalized_locale =="en_US";
+}
+
 HotwordService::HotwordService(Profile* profile)
     : profile_(profile) {
 }
@@ -72,19 +87,7 @@ bool HotwordService::IsServiceAvailable() {
 bool HotwordService::IsHotwordAllowed() {
   std::string group = base::FieldTrialList::FindFullName(
       hotword_internal::kHotwordFieldTrialName);
-  if (!group.empty() &&
-      group != hotword_internal::kHotwordFieldTrialDisabledGroupName) {
-    std::string locale =
-#if defined(OS_CHROMEOS)
-        // On ChromeOS locale is per-profile.
-        profile_->GetPrefs()->GetString(prefs::kApplicationLocale);
-#else
-        g_browser_process->GetApplicationLocale();
-#endif
-    // Only available for English now.
-    std::string normalized_locale = l10n_util::NormalizeLocale(locale);
-    return normalized_locale == "en" || normalized_locale == "en_us" ||
-        normalized_locale =="en_US";
-  }
-  return false;
+  return !group.empty() &&
+      group != hotword_internal::kHotwordFieldTrialDisabledGroupName &&
+      DoesHotwordSupportLanguage(profile_);
 }
diff --git a/chrome/browser/search/hotword_service.h b/chrome/browser/search/hotword_service.h
index 6dbd6cd..ef587a3 100644
--- a/chrome/browser/search/hotword_service.h
+++ b/chrome/browser/search/hotword_service.h
@@ -20,6 +20,9 @@ extern const char kHotwordFieldTrialDisabledGroupName[];
 // search.
 class HotwordService : public BrowserContextKeyedService {
  public:
+  // Returns true if the hotword supports the current system language.
+  static bool DoesHotwordSupportLanguage(Profile* profile);
+
   explicit HotwordService(Profile* profile);
   virtual ~HotwordService();
 
diff --git a/chrome/browser/ui/app_list/app_list_view_delegate.cc b/chrome/browser/ui/app_list/app_list_view_delegate.cc
index 2de89ad..0c2b274 100644
--- a/chrome/browser/ui/app_list/app_list_view_delegate.cc
+++ b/chrome/browser/ui/app_list/app_list_view_delegate.cc
@@ -35,7 +35,6 @@
 #include "content/public/browser/page_navigator.h"
 #include "content/public/browser/user_metrics.h"
 #include "grit/theme_resources.h"
-#include "ui/app_list/app_list_switches.h"
 #include "ui/app_list/app_list_view_delegate_observer.h"
 #include "ui/app_list/search_box_model.h"
 #include "ui/app_list/speech_ui_model.h"
@@ -96,15 +95,10 @@ AppListViewDelegate::AppListViewDelegate(Profile* profile,
   RegisterForNotifications();
   g_browser_process->profile_manager()->GetProfileInfoCache().AddObserver(this);
 
-  // Hotword listening is on by default in ChromeOS right now. Here shouldn't
-  // use the current state in the webui because it will be changed to 'hotword
-  // listening' state from 'ready' after the view is initialized.
+  app_list::StartPageService* service =
+      app_list::StartPageService::Get(profile_);
   speech_ui_.reset(new app_list::SpeechUIModel(
-#if defined(OS_CHROMEOS)
-      app_list::switches::IsVoiceSearchEnabled() ?
-        app_list::SPEECH_RECOGNITION_HOTWORD_LISTENING :
-#endif
-        app_list::SPEECH_RECOGNITION_OFF));
+      service ? service->state() : app_list::SPEECH_RECOGNITION_OFF));
 
 #if defined(GOOGLE_CHROME_BUILD)
   speech_ui_->set_logo(
@@ -113,8 +107,6 @@ AppListViewDelegate::AppListViewDelegate(Profile* profile,
 #endif
 
   OnProfileChanged();  // sets model_
-  app_list::StartPageService* service =
-      app_list::StartPageService::Get(profile_);
   if (service)
     service->AddObserver(this);
 }
diff --git a/chrome/browser/ui/app_list/start_page_service.cc b/chrome/browser/ui/app_list/start_page_service.cc
index 151bd65..6c897bf 100644
--- a/chrome/browser/ui/app_list/start_page_service.cc
+++ b/chrome/browser/ui/app_list/start_page_service.cc
@@ -9,16 +9,13 @@
 #include "base/command_line.h"
 #include "base/memory/singleton.h"
 #include "chrome/browser/chrome_notification_types.h"
-#include "chrome/browser/extensions/extension_system_factory.h"
-#include "chrome/browser/extensions/install_tracker_factory.h"
 #include "chrome/browser/media/media_stream_infobar_delegate.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/app_list/recommended_apps.h"
 #include "chrome/browser/ui/app_list/start_page_observer.h"
+#include "chrome/browser/ui/app_list/start_page_service_factory.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/url_constants.h"
-#include "components/browser_context_keyed_service/browser_context_dependency_manager.h"
-#include "components/browser_context_keyed_service/browser_context_keyed_service_factory.h"
 #include "content/public/browser/notification_details.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
@@ -31,46 +28,6 @@
 
 namespace app_list {
 
-class StartPageService::Factory : public BrowserContextKeyedServiceFactory {
- public:
-  static StartPageService* GetForProfile(Profile* profile) {
-    if (!CommandLine::ForCurrentProcess()->HasSwitch(
-            ::switches::kShowAppListStartPage) &&
-        !app_list::switches::IsVoiceSearchEnabled()) {
-      return NULL;
-    }
-
-    return static_cast<StartPageService*>(
-        GetInstance()->GetServiceForBrowserContext(profile, true));
-  }
-
-  static Factory* GetInstance() {
-    return Singleton<Factory>::get();
-  }
-
- private:
-  friend struct DefaultSingletonTraits<Factory>;
-
-  Factory()
-      : BrowserContextKeyedServiceFactory(
-            "AppListStartPageService",
-            BrowserContextDependencyManager::GetInstance()) {
-    DependsOn(extensions::ExtensionSystemFactory::GetInstance());
-    DependsOn(extensions::InstallTrackerFactory::GetInstance());
-  }
-
-  virtual ~Factory() {}
-
-  // BrowserContextKeyedServiceFactory overrides:
-  virtual BrowserContextKeyedService* BuildServiceInstanceFor(
-      content::BrowserContext* context) const OVERRIDE {
-     Profile* profile = static_cast<Profile*>(context);
-     return new StartPageService(profile);
-  }
-
-  DISALLOW_COPY_AND_ASSIGN(Factory);
-};
-
 class StartPageService::ProfileDestroyObserver
     : public content::NotificationObserver {
  public:
@@ -118,13 +75,22 @@ class StartPageService::StartPageWebContentsDelegate
 
 // static
 StartPageService* StartPageService::Get(Profile* profile) {
-  return Factory::GetForProfile(profile);
+  return StartPageServiceFactory::GetForProfile(profile);
 }
 
 StartPageService::StartPageService(Profile* profile)
     : profile_(profile),
       profile_destroy_observer_(new ProfileDestroyObserver(this)),
-      recommended_apps_(new RecommendedApps(profile)) {
+      recommended_apps_(new RecommendedApps(profile)),
+      state_(app_list::SPEECH_RECOGNITION_OFF) {
+#if defined(OS_CHROMEOS)
+  // Updates the default state to hotword listening, because this is
+  // the default behavior. This will be updated when the page is loaded and
+  // the nacl module is loaded.
+  if (app_list::switches::IsVoiceSearchEnabled())
+    state_ = app_list::SPEECH_RECOGNITION_HOTWORD_LISTENING;
+#endif
+
   contents_.reset(content::WebContents::Create(
       content::WebContents::CreateParams(profile_)));
   contents_delegate_.reset(new StartPageWebContentsDelegate());
@@ -183,6 +149,7 @@ void StartPageService::OnSpeechSoundLevelChanged(int16 level) {
 
 void StartPageService::OnSpeechRecognitionStateChanged(
     SpeechRecognitionState new_state) {
+  state_ = new_state;
   FOR_EACH_OBSERVER(StartPageObserver,
                     observers_,
                     OnSpeechRecognitionStateChanged(new_state));
diff --git a/chrome/browser/ui/app_list/start_page_service.h b/chrome/browser/ui/app_list/start_page_service.h
index bd21967..d1be3e7 100644
--- a/chrome/browser/ui/app_list/start_page_service.h
+++ b/chrome/browser/ui/app_list/start_page_service.h
@@ -48,13 +48,13 @@ class StartPageService : public BrowserContextKeyedService {
 
   RecommendedApps* recommended_apps() { return recommended_apps_.get(); }
   Profile* profile() { return profile_; }
+  SpeechRecognitionState state() { return state_; }
   void OnSpeechResult(const base::string16& query, bool is_final);
   void OnSpeechSoundLevelChanged(int16 level);
   void OnSpeechRecognitionStateChanged(SpeechRecognitionState new_state);
 
  private:
-  // A BrowserContextKeyedServiceFactory for this service.
-  class Factory;
+  friend class StartPageServiceFactory;
 
   // ProfileDestroyObserver to shutdown the service on exiting. WebContents
   // depends on the profile and needs to be closed before the profile and its
@@ -76,6 +76,7 @@ class StartPageService : public BrowserContextKeyedService {
   scoped_ptr<StartPageWebContentsDelegate> contents_delegate_;
   scoped_ptr<ProfileDestroyObserver> profile_destroy_observer_;
   scoped_ptr<RecommendedApps> recommended_apps_;
+  SpeechRecognitionState state_;
   ObserverList<StartPageObserver> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(StartPageService);
diff --git a/chrome/browser/ui/app_list/start_page_service_factory.cc b/chrome/browser/ui/app_list/start_page_service_factory.cc
new file mode 100644
index 0000000..0e65866
--- /dev/null
+++ b/chrome/browser/ui/app_list/start_page_service_factory.cc
@@ -0,0 +1,63 @@
+// Copyright 2014 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/app_list/start_page_service_factory.h"
+
+#include "base/command_line.h"
+#include "chrome/browser/extensions/extension_system_factory.h"
+#include "chrome/browser/extensions/install_tracker_factory.h"
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/ui/app_list/start_page_service.h"
+#include "chrome/common/chrome_switches.h"
+#include "chrome/common/pref_names.h"
+#include "components/browser_context_keyed_service/browser_context_dependency_manager.h"
+#include "components/user_prefs/pref_registry_syncable.h"
+#include "ui/app_list/app_list_switches.h"
+
+namespace app_list {
+
+// static
+StartPageService* StartPageServiceFactory::GetForProfile(Profile* profile) {
+  if (!CommandLine::ForCurrentProcess()->HasSwitch(
+          ::switches::kShowAppListStartPage) &&
+      !app_list::switches::IsVoiceSearchEnabled()) {
+      return NULL;
+    }
+
+  return static_cast<StartPageService*>(
+      GetInstance()->GetServiceForBrowserContext(profile, true));
+}
+
+// static
+StartPageServiceFactory* StartPageServiceFactory::GetInstance() {
+  return Singleton<StartPageServiceFactory>::get();
+}
+
+StartPageServiceFactory::StartPageServiceFactory()
+    : BrowserContextKeyedServiceFactory(
+        "AppListStartPageService",
+        BrowserContextDependencyManager::GetInstance()) {
+  DependsOn(extensions::ExtensionSystemFactory::GetInstance());
+  DependsOn(extensions::InstallTrackerFactory::GetInstance());
+}
+
+StartPageServiceFactory::~StartPageServiceFactory() {}
+
+BrowserContextKeyedService* StartPageServiceFactory::BuildServiceInstanceFor(
+    content::BrowserContext* context) const {
+  Profile* profile = static_cast<Profile*>(context);
+  return new StartPageService(profile);
+}
+
+void StartPageServiceFactory::RegisterProfilePrefs(
+    user_prefs::PrefRegistrySyncable* registry) {
+#if defined(OS_CHROMEOS)
+  registry->RegisterBooleanPref(
+      prefs::kHotwordAppListEnabled,
+      true,
+      user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
+#endif
+}
+
+}  // namespace app_list
diff --git a/chrome/browser/ui/app_list/start_page_service_factory.h b/chrome/browser/ui/app_list/start_page_service_factory.h
new file mode 100644
index 0000000..01ee036
--- /dev/null
+++ b/chrome/browser/ui/app_list/start_page_service_factory.h
@@ -0,0 +1,42 @@
+// Copyright 2014 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_APP_LIST_START_PAGE_SERVICE_FACTORY_H_
+#define CHROME_BROWSER_UI_APP_LIST_START_PAGE_SERVICE_FACTORY_H_
+
+#include "base/memory/singleton.h"
+#include "components/browser_context_keyed_service/browser_context_keyed_service_factory.h"
+
+class Profile;
+
+namespace app_list {
+class StartPageService;
+
+// Singleton factory to create StartPageService.
+class StartPageServiceFactory : public BrowserContextKeyedServiceFactory {
+ public:
+  // Gets or creates the instance of StartPageService for |profile|.
+  static StartPageService* GetForProfile(Profile* profile);
+
+  // Gets the singleton instance of this factory.
+  static StartPageServiceFactory* GetInstance();
+
+ private:
+  friend struct DefaultSingletonTraits<StartPageServiceFactory>;
+
+  StartPageServiceFactory();
+  virtual ~StartPageServiceFactory();
+
+  // BrowserContextKeyedServiceFactory overrides:
+  virtual BrowserContextKeyedService* BuildServiceInstanceFor(
+      content::BrowserContext* context) const OVERRIDE;
+  virtual void RegisterProfilePrefs(
+      user_prefs::PrefRegistrySyncable* registry) OVERRIDE;
+
+  DISALLOW_COPY_AND_ASSIGN(StartPageServiceFactory);
+};
+
+}  // namespace app_list
+
+#endif  // CHROME_BROWSER_UI_APP_LIST_START_PAGE_SERVICE_FACTORY_H_
diff --git a/chrome/browser/ui/webui/app_list/start_page_handler.cc b/chrome/browser/ui/webui/app_list/start_page_handler.cc
index 976cc18..d38aa3e 100644
--- a/chrome/browser/ui/webui/app_list/start_page_handler.cc
+++ b/chrome/browser/ui/webui/app_list/start_page_handler.cc
@@ -8,10 +8,12 @@
 
 #include "base/bind.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/prefs/pref_service.h"
 #include "base/sys_info.h"
 #include "base/values.h"
 #include "chrome/browser/extensions/extension_service.h"
 #include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/search/hotword_service.h"
 #include "chrome/browser/ui/app_list/app_list_controller_delegate.h"
 #include "chrome/browser/ui/app_list/app_list_service.h"
 #include "chrome/browser/ui/app_list/recommended_apps.h"
@@ -19,6 +21,7 @@
 #include "chrome/browser/ui/host_desktop.h"
 #include "chrome/browser/ui/webui/extensions/extension_icon_source.h"
 #include "chrome/common/extensions/extension_icon_set.h"
+#include "chrome/common/pref_names.h"
 #include "content/public/browser/web_contents_view.h"
 #include "content/public/browser/web_ui.h"
 #include "extensions/browser/extension_system.h"
@@ -97,6 +100,36 @@ void StartPageHandler::SendRecommendedApps() {
                                    recommended_list);
 }
 
+#if defined(OS_CHROMEOS)
+bool StartPageHandler::HotwordEnabled() {
+  Profile* profile = Profile::FromWebUI(web_ui());
+  return HotwordService::DoesHotwordSupportLanguage(profile) &&
+      profile->GetPrefs()->GetBoolean(prefs::kHotwordAppListEnabled);
+}
+
+void StartPageHandler::OnHotwordEnabledChanged() {
+  web_ui()->CallJavascriptFunction(
+      "appList.startPage.setHotwordEnabled",
+      base::FundamentalValue(HotwordEnabled()));
+}
+
+void StartPageHandler::SynchronizeHotwordEnabled() {
+  Profile* profile = Profile::FromWebUI(web_ui());
+  PrefService* pref_service = profile->GetPrefs();
+  const PrefService::Preference* pref =
+      pref_service->FindPreference(prefs::kHotwordSearchEnabled);
+  if (!pref || pref->IsDefaultValue())
+    return;
+
+  bool search_enabled = false;
+  if (!pref->GetValue()->GetAsBoolean(&search_enabled))
+    return;
+
+  if (pref_service->GetBoolean(prefs::kHotwordAppListEnabled) != search_enabled)
+    pref_service->SetBoolean(prefs::kHotwordAppListEnabled, search_enabled);
+}
+#endif
+
 void StartPageHandler::HandleInitialize(const base::ListValue* args) {
   Profile* profile = Profile::FromWebUI(web_ui());
   StartPageService* service = StartPageService::Get(profile);
@@ -109,11 +142,20 @@ void StartPageHandler::HandleInitialize(const base::ListValue* args) {
   SendRecommendedApps();
 
 #if defined(OS_CHROMEOS)
-  // TODO(mukai): respect the configuration of the availability of the hotword
-  // plugin.
   if (app_list::switches::IsVoiceSearchEnabled() &&
+      HotwordService::DoesHotwordSupportLanguage(profile) &&
       base::SysInfo::IsRunningOnChromeOS()) {
-    web_ui()->CallJavascriptFunction("appList.startPage.maybeInitializePlugin");
+    SynchronizeHotwordEnabled();
+    OnHotwordEnabledChanged();
+    pref_change_registrar_.Init(profile->GetPrefs());
+    pref_change_registrar_.Add(
+        prefs::kHotwordSearchEnabled,
+        base::Bind(&StartPageHandler::SynchronizeHotwordEnabled,
+                   base::Unretained(this)));
+    pref_change_registrar_.Add(
+        prefs::kHotwordAppListEnabled,
+        base::Bind(&StartPageHandler::OnHotwordEnabledChanged,
+                   base::Unretained(this)));
   }
 #endif
 }
diff --git a/chrome/browser/ui/webui/app_list/start_page_handler.h b/chrome/browser/ui/webui/app_list/start_page_handler.h
index c3d35bb..b444f75 100644
--- a/chrome/browser/ui/webui/app_list/start_page_handler.h
+++ b/chrome/browser/ui/webui/app_list/start_page_handler.h
@@ -7,6 +7,7 @@
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
+#include "base/prefs/pref_change_registrar.h"
 #include "chrome/browser/ui/app_list/recommended_apps_observer.h"
 #include "content/public/browser/web_ui_message_handler.h"
 
@@ -35,6 +36,18 @@ class StartPageHandler : public content::WebUIMessageHandler,
   // Creates a ListValue for the recommended apps and sends it to js side.
   void SendRecommendedApps();
 
+#if defined(OS_CHROMEOS)
+  // Returns true if the hotword is enabled.
+  bool HotwordEnabled();
+
+  // Called when the pref has been changed.
+  void OnHotwordEnabledChanged();
+
+  // Called when the availability of the hotword for NTP is changed. The new
+  // value has to be propagated.
+  void SynchronizeHotwordEnabled();
+#endif
+
   // JS callbacks.
   void HandleInitialize(const base::ListValue* args);
   void HandleLaunchApp(const base::ListValue* args);
@@ -43,6 +56,7 @@ class StartPageHandler : public content::WebUIMessageHandler,
   void HandleSpeechRecognition(const base::ListValue* args);
 
   RecommendedApps* recommended_apps_;  // Not owned.
+  PrefChangeRegistrar pref_change_registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(StartPageHandler);
 };
diff --git a/chrome/browser/ui/webui/options/browser_options_handler.cc b/chrome/browser/ui/webui/options/browser_options_handler.cc
index 5be4f54..b648de91 100644
--- a/chrome/browser/ui/webui/options/browser_options_handler.cc
+++ b/chrome/browser/ui/webui/options/browser_options_handler.cc
@@ -379,6 +379,7 @@ void BrowserOptionsHandler::GetLocalizedValues(base::DictionaryValue* values) {
       IDS_OPTIONS_SETTINGS_ACCESSIBILITY_AUTOCLICK_DELAY_VERY_LONG },
     { "enableContentProtectionAttestation",
       IDS_OPTIONS_ENABLE_CONTENT_PROTECTION_ATTESTATION },
+    { "enableHotwordAppList", IDS_OPTIONS_ENABLE_HOTWORD_APP_LIST },
     { "factoryResetHeading", IDS_OPTIONS_FACTORY_RESET_HEADING },
     { "factoryResetTitle", IDS_OPTIONS_FACTORY_RESET },
     { "factoryResetRestart", IDS_OPTIONS_FACTORY_RESET_BUTTON },
@@ -546,6 +547,12 @@ void BrowserOptionsHandler::GetLocalizedValues(base::DictionaryValue* values) {
   magnifier_list->Append(option_partial.release());
 
   values->Set("magnifierList", magnifier_list.release());
+
+  scoped_ptr<base::FundamentalValue> should_show_app_list_hotword(
+      new base::FundamentalValue(
+          HotwordService::DoesHotwordSupportLanguage(profile)));
+  values->Set(
+      "shouldShowAppListHotword", should_show_app_list_hotword.release());
 #endif
 
 #if defined(OS_MACOSX)
@@ -867,9 +874,9 @@ void BrowserOptionsHandler::InitializePage() {
         "BrowserOptions.enableFactoryResetSection");
   }
 
+  Profile* profile = Profile::FromWebUI(web_ui());
   OnAccountPictureManagedChanged(
-      policy::ProfilePolicyConnectorFactory::GetForProfile(
-          Profile::FromWebUI(web_ui()))->
+      policy::ProfilePolicyConnectorFactory::GetForProfile(profile)->
           policy_service()->GetPolicies(
               policy::PolicyNamespace(policy::POLICY_DOMAIN_CHROME,
                                       std::string()))
diff --git a/chrome/chrome_browser_ui.gypi b/chrome/chrome_browser_ui.gypi
index 8f093d2..9408442 100644
--- a/chrome/chrome_browser_ui.gypi
+++ b/chrome/chrome_browser_ui.gypi
@@ -237,6 +237,8 @@
         'browser/ui/app_list/start_page_observer.h',
         'browser/ui/app_list/start_page_service.cc',
         'browser/ui/app_list/start_page_service.h',
+        'browser/ui/app_list/start_page_service_factory.cc',
+        'browser/ui/app_list/start_page_service_factory.h',
         'browser/ui/app_modal_dialogs/app_modal_dialog.cc',
         'browser/ui/app_modal_dialogs/app_modal_dialog.h',
         'browser/ui/app_modal_dialogs/app_modal_dialog_queue.cc',
diff --git a/chrome/common/pref_names.cc b/chrome/common/pref_names.cc
index 22dbe44..fd79501 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -2148,6 +2148,13 @@ const char kHotwordSearchEnabled[] = "hotword.search_enabled";
 // longer shown.
 const char kHotwordOptInPopupTimesShown[] = "hotword.opt_in_popup_times_shown";
 
+#if defined(OS_CHROMEOS)
+// A boolean pref that controls the enabled-state of hotword search in the
+// app-list. This pref cooperates with kHotwordSearchEnabled. If the user
+// explicitly turns off kHotwordSearchEnabled, this pref should go off too.
+const char kHotwordAppListEnabled[] = "hotword.app_list_enabled";
+#endif
+
 #if defined(OS_ANDROID)
 // Boolean that controls the global enabled-state of protected media identifier.
 const char kProtectedMediaIdentifierEnabled[] =
diff --git a/chrome/common/pref_names.h b/chrome/common/pref_names.h
index 4508496..27930f8 100644
--- a/chrome/common/pref_names.h
+++ b/chrome/common/pref_names.h
@@ -740,6 +740,10 @@ extern const char kVideoCaptureAllowedUrls[];
 extern const char kHotwordSearchEnabled[];
 extern const char kHotwordOptInPopupTimesShown[];
 
+#if defined(OS_CHROMEOS)
+extern const char kHotwordAppListEnabled[];
+#endif
+
 #if defined(OS_ANDROID)
 extern const char kProtectedMediaIdentifierEnabled[];
 #endif