flags: expire M78 & earlier flags

This change will be merged to the M79 branch in keeping with the flag
deprecation rollout strategy:

* M78 expires flags set for 76 & earlier
* M79 expires flags set for 78 & earlier
* M80 expires flags set for 80 & earlier
* MXX expires flags set for XX & earlier onward

Bug: 1019714
Change-Id: Ic789610160f1de11715ed41d6ff153a71487a08d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1890814
Reviewed-by: Nico Weber <[email protected]>
Commit-Queue: Elly Fong-Jones <[email protected]>
Cr-Commit-Position: refs/heads/master@{#711417}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index bfc6e4d..3b80773 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1270,6 +1270,8 @@
 
 extern const char kUnexpireFlagsM76Name[];
 extern const char kUnexpireFlagsM76Description[];
+extern const char kUnexpireFlagsM78Name[];
+extern const char kUnexpireFlagsM78Description[];
 
 extern const char kUnsafeWebGPUName[];
 extern const char kUnsafeWebGPUDescription[];