Add --enable-hdr to about:flags

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 1004 matching lines @@
 extern const char kBootAnimationDescription[];
 
 #endif  // defined(OS_CHROMEOS)
 
 // Name of the flag for accelerated video decode where available.
 extern const char kAcceleratedVideoDecodeName[];
 
 // Description for the flag for accelerated video decode where available.
 extern const char kAcceleratedVideoDecodeDescription[];
 
+// Name/Description for the "enable-hdr" flag.
+extern const char kEnableHDRName[];
+extern const char kEnableHDRDescription[];
+
 // Name for the flag for cloud import feature.
 extern const char kCloudImport[];
 
 // Description for the flag for cloud import.
 extern const char kCloudImportDescription[];
 
 // Name for the flag to set to enable Request Tablet Site in the wrench menu.
 extern const char kRequestTabletSiteName[];
 
 // Description for the flag to set to enable Request Tablet Site in the wrench
@@ skipping 2093 matching lines @@
 
 // Description of the about: flag enabling emoji, handwriting and voice input on
 // opt-in IME menu.
 extern const char kEnableEhvInputDescription[];
 
 #endif  // #if defined(OS_CHROMEOS)
 
 }  // namespace flag_descriptions
 
 #endif  // CHROME_BROWSER_FLAG_DESCRIPTIONS_H_