Enable chrome://discards on Linux.

chrome/common/url_constants.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.
 
 // Contains constants for known URLs and portions thereof.
 
 #ifndef CHROME_COMMON_URL_CONSTANTS_H_
 #define CHROME_COMMON_URL_CONSTANTS_H_
 
 #include <stddef.h>
@@ skipping 121 matching lines @@
 extern const char kChromeUIWebRtcLogsURL[];
 #endif
 
 #if defined(ENABLE_MEDIA_ROUTER)
 extern const char kChromeUIMediaRouterURL[];
 #if defined(OS_WIN) || defined(OS_MACOSX) || defined(OS_CHROMEOS)
 extern const char kChromeUICastURL[];
 #endif
 #endif
 
-#if defined(OS_WIN) || defined(OS_MACOSX) || defined(OS_CHROMEOS)
+#if defined(OS_WIN) || defined(OS_MACOSX) || defined(OS_LINUX)
 extern const char kChromeUIDiscardsHost[];
 extern const char kChromeUIDiscardsURL[];
 #endif
 
 // chrome components of URLs. Should be kept in sync with the full URLs above.
 extern const char kChromeUIAboutHost[];
 extern const char kChromeUIAboutPageFrameHost[];
 extern const char kChromeUIBlankHost[];
 extern const char kChromeUIAppLauncherPageHost[];
 extern const char kChromeUIAppListStartPageHost[];
@@ skipping 450 matching lines @@
 extern const char kChooserUsbOverviewURL[];
 
 #if defined(OS_CHROMEOS)
 // The URL for EOL notification
 extern const char kEolNotificationURL[];
 #endif
 
 }  // namespace chrome
 
 #endif  // CHROME_COMMON_URL_CONSTANTS_H_