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

chrome/common/pref_names.cc

Index: chrome/common/pref_names.cc
diff --git a/chrome/common/pref_names.cc b/chrome/common/pref_names.cc
index ab0b57d7afc11cb0ed5514d23b36fe4714f89d73..108a781bebff9a7331cbb6d697db072e0e40d622 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -1855,6 +1855,11 @@ const char kHotwordSearchEnabled[] = "hotword.search_enabled_2";
 // seconds of audio data before is sent back to improve voice search.
 const char kHotwordAudioLoggingEnabled[] = "hotword.audio_logging_enabled";
 
+// A string holding the locale information under which Hotword was installed.
+// It is used for comparison since the hotword voice search trigger must be
+// reinstalled to handle a new language.
+const char kHotwordPreviousLanguage[] = "hotword.previous_language";
+
 #if defined(OS_ANDROID)
 // Boolean that controls the global enabled-state of protected media identifier.
 const char kProtectedMediaIdentifierEnabled[] =