[Hotword] Uninstall and reinstall the extension upon language change.

chrome/common/pref_names.h

 // Copyright (c) 2012 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.
 
 // Constants for the names of various preferences, for easier changing.
 
 #ifndef CHROME_COMMON_PREF_NAMES_H_
 #define CHROME_COMMON_PREF_NAMES_H_
 
 #include <stddef.h>
@@ skipping 637 matching lines @@
 extern const char kManagedNotificationsBlockedForUrls[];
 extern const char kManagedAutoSelectCertificateForUrls[];
 
 extern const char kAudioCaptureAllowed[];
 extern const char kAudioCaptureAllowedUrls[];
 extern const char kVideoCaptureAllowed[];
 extern const char kVideoCaptureAllowedUrls[];
 
 extern const char kHotwordSearchEnabled[];
 extern const char kHotwordAudioLoggingEnabled[];
+extern const char kHotwordPreviousLanguage[];
 
 #if defined(OS_ANDROID)
 extern const char kProtectedMediaIdentifierEnabled[];
 #endif
 
 #if defined(OS_CHROMEOS)
 extern const char kDeviceSettingsCache[];
 extern const char kHardwareKeyboardLayout[];
 extern const char kCarrierDealPromoShown[];
 extern const char kShouldAutoEnroll[];
@@ skipping 162 matching lines @@
 
 #if defined(OS_ANDROID)
 extern const char kPartnerBookmarkMappings[];
 #endif
 
 extern const char kQuickCheckEnabled[];
 
 }  // namespace prefs
 
 #endif  // CHROME_COMMON_PREF_NAMES_H_