Add --enable-hdr to about:flags

chrome/browser/flag_descriptions.h

Index: chrome/browser/flag_descriptions.h
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 9e97ec7c9d7d892dd9a82f229e86008569aca074..8de94dfb3850451f9b929304cd6698fa68df0c6b 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1022,6 +1022,10 @@ 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[];