Get signals working in the EXTRA_DATA section of MHTML

chrome/browser/flag_descriptions.h

 // Copyright 2017 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.
 
 #ifndef CHROME_BROWSER_FLAG_DESCRIPTIONS_H_
 #define CHROME_BROWSER_FLAG_DESCRIPTIONS_H_
 
 // Includes needed for macros allowing conditional compilation of some strings.
 #include "build/build_config.h"
 #include "build/buildflag.h"
@@ skipping 2242 matching lines @@
 extern const char kOfflinePagesAsyncDownloadDescription[];
 
 // Name for the flag to enable concurrent background loading on svelte (512MB
 // RAM) devices.
 extern const char kOfflinePagesSvelteConcurrentLoadingName[];
 
 // Description for the flag to enable concurrent background loading on svelte
 // (512MB RAM) devices.
 extern const char kOfflinePagesSvelteConcurrentLoadingDescription[];
 
+// Name for the flag to enable collecting load completeness signals to improve
+// prerendering snapshot timing.
+extern const char kOfflinePagesLoadSignalCollectingName[];
+
+// Description for the flag to enable collecting load timing signals to improve
+// prerendering snapshot timing.
+extern const char kOfflinePagesLoadSignalCollectingDescription[];
+
 // Name for the flag to enable offline pages to be prefetched.
 extern const char kOfflinePagesPrefetchingName[];
 
 // Description for the flag to enable offline pages prefetching.
 extern const char kOfflinePagesPrefetchingDescription[];
 
 // Name for the flag to enable offline pages to be shared.
 extern const char kOfflinePagesSharingName[];
 
 // Description for the flag to enable offline pages sharing.
@@ skipping 933 matching lines @@
 extern const char kEnableCopylessPasteName[];
 
 // Description of the flag that enables Copyless Paste.
 extern const char kEnableCopylessPasteDescription[];
 
 #endif  // defined(OS_ANDROID)
 
 }  // namespace flag_descriptions
 
 #endif  // CHROME_BROWSER_FLAG_DESCRIPTIONS_H_