Disable new hotwording in the launcher for non-ChromeOS.

Voice input in general is unsupported in the launcher for non-ChromeOS.

BUG=397019

Review URL: https://codereview.chromium.org/721093002

Cr-Commit-Position: refs/heads/master@{#304003}

chrome/browser/ui/app_list/start_page_service.cc

@@ -202,13 +202,15 @@ void StartPageService::ToggleSpeechRecognition() {
 }
 
 bool StartPageService::HotwordEnabled() {
+// Voice input for the launcher is unsupported on non-ChromeOS platforms.
+// TODO(amistry): Make speech input, and hotwording, work on non-ChromeOS.
+#if defined(OS_CHROMEOS)
   if (HotwordService::IsExperimentalHotwordingEnabled()) {
     auto prefs = profile_->GetPrefs();
     return HotwordServiceFactory::IsServiceAvailable(profile_) &&
         (prefs->GetBoolean(prefs::kHotwordSearchEnabled) ||
          prefs->GetBoolean(prefs::kHotwordAlwaysOnSearchEnabled));
   }
-#if defined(OS_CHROMEOS)
   return HotwordServiceFactory::IsServiceAvailable(profile_) &&
       profile_->GetPrefs()->GetBoolean(prefs::kHotwordSearchEnabled);
 #else