Add build flag to disable hotwording.

chrome/browser/search/hotword_service.cc

 // Copyright 2013 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/search/hotword_service.h"
 
 #include <string>
 
 #include "base/command_line.h"
 #include "base/i18n/case_conversion.h"
@@ skipping 624 matching lines @@
     bool audio_capture_allowed =
         profile_->GetPrefs()->GetBoolean(prefs::kAudioCaptureAllowed);
     if (!audio_capture_allowed || !microphone_available_)
       error_message_ = IDS_HOTWORD_MICROPHONE_ERROR_MESSAGE;
   }
 
   return (error_message_ == 0) && IsHotwordAllowed();
 }
 
 bool HotwordService::IsHotwordAllowed() {
+#if defined(ENABLE_HOTWORDING)
   std::string group = base::FieldTrialList::FindFullName(
       hotword_internal::kHotwordFieldTrialName);
   // Allow hotwording by default, and only disable if the field trial has been
   // set.
   if (group == hotword_internal::kHotwordFieldTrialDisabledGroupName)
     return false;
 
   return DoesHotwordSupportLanguage(profile_);
+#else
+  return false;
+#endif
 }
 
 bool HotwordService::IsOptedIntoAudioLogging() {
   // Do not opt the user in if the preference has not been set.
   return
       profile_->GetPrefs()->HasPrefPath(prefs::kHotwordAudioLoggingEnabled) &&
       profile_->GetPrefs()->GetBoolean(prefs::kHotwordAudioLoggingEnabled);
 }
 
 bool HotwordService::IsAlwaysOnEnabled() {
@@ skipping 212 matching lines @@
   // Only support multiple profiles and profile switching in ChromeOS.
   if (user_manager::UserManager::IsInitialized()) {
     user_manager::User* user =
         user_manager::UserManager::Get()->GetActiveUser();
     if (user && user->is_profile_created())
       return profile_ == ProfileManager::GetActiveUserProfile();
   }
 #endif
   return true;
 }