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.cc b/chrome/browser/flag_descriptions.cc
index 10669c16..6b767b5 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -2171,6 +2171,10 @@
 const char kUnexpireFlagsM76Description[] =
     "Temporarily unexpire flags that are expired as of M76. These flags will "
     "be removed soon.";
+const char kUnexpireFlagsM78Name[] = "Temporarily unexpire M78 flags.";
+const char kUnexpireFlagsM78Description[] =
+    "Temporarily unexpire flags that are expired as of M78. These flags will "
+    "be removed soon.";
 
 const char kUnsafeWebGPUName[] = "Unsafe WebGPU";
 const char kUnsafeWebGPUDescription[] =