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/+/1890814Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#711417}

chrome/browser/about_flags.cc

@@ -4415,6 +4415,9 @@ const FeatureEntry kFeatureEntries[] = {
     {"temporary-unexpire-flags-m76", flag_descriptions::kUnexpireFlagsM76Name,
      flag_descriptions::kUnexpireFlagsM76Description, kOsAll,
      FEATURE_VALUE_TYPE(flags::kUnexpireFlagsM76)},
+    {"temporary-unexpire-flags-m78", flag_descriptions::kUnexpireFlagsM78Name,
+     flag_descriptions::kUnexpireFlagsM78Description, kOsAll,
+     FEATURE_VALUE_TYPE(flags::kUnexpireFlagsM78)},
 
 #if defined(OS_CHROMEOS)
     {"lock-screen-media-controls",

chrome/browser/flag-metadata.json

@@ -3320,6 +3320,11 @@
     "owners": [ "ellyjones", "flags-dev" ],
     "expiry_milestone": 80
   },
+  {
+    "name": "temporary-unexpire-flags-m78",
+    "owners": [ "ellyjones", "flags-dev" ],
+    "expiry_milestone": 81
+  },
   {
     "name": "terminal-system-app",
     "owners": [ "joelhockey", "benwells", "//chrome/browser/chromeos/guest_os/OWNERS" ],

chrome/browser/flag_descriptions.cc

@@ -2171,6 +2171,10 @@ const char kUnexpireFlagsM76Name[] = "Temporarily unexpire M76 flags.";
 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[] =

chrome/browser/flag_descriptions.h

@@ -1270,6 +1270,8 @@ extern const char kTurnOffStreamingMediaCachingDescription[];
 
 extern const char kUnexpireFlagsM76Name[];
 extern const char kUnexpireFlagsM76Description[];
+extern const char kUnexpireFlagsM78Name[];
+extern const char kUnexpireFlagsM78Description[];
 
 extern const char kUnsafeWebGPUName[];
 extern const char kUnsafeWebGPUDescription[];

chrome/browser/unexpire_flags.cc

@@ -36,6 +36,8 @@ class FlagPredicateSingleton {
 
 const base::Feature kUnexpireFlagsM76{"TemporaryUnexpireFlagsM76",
                                       base::FEATURE_DISABLED_BY_DEFAULT};
+const base::Feature kUnexpireFlagsM78{"TemporaryUnexpireFlagsM78",
+                                      base::FEATURE_DISABLED_BY_DEFAULT};
 
 bool ExpiryEnabledForMstone(int mstone) {
   // generate_expired_list.py will never emit flags with expiry milestone -1, to
@@ -49,14 +51,17 @@ bool ExpiryEnabledForMstone(int mstone) {
   if (mstone == -1)
     return false;
 
-  // Currently expiration targets flags expiring in M76 or earlier. In M79 this
-  // will become M78 or earlier; in M80 it will become M80 or earlier, and in
-  // all future milestones Mx it will be Mx or earlier, so this logic will cease
-  // to hardcode a milestone and instead target the current major version.
+  // In M78 this expired flags with their expirations set to M76 or earlier.
+  // In M79 this expires flags with their expirations set to M78 or earlier.
+  // In M80 and later, this will expire any flags whose expiration is <= the
+  // current mstone, and this block comment will go away along with these
+  // special cases.
   if (mstone < 76)
     return true;
   if (mstone == 76)
     return !base::FeatureList::IsEnabled(kUnexpireFlagsM76);
+  if (mstone == 77 || mstone == 78)
+    return !base::FeatureList::IsEnabled(kUnexpireFlagsM78);
   return false;
 }
 

chrome/browser/unexpire_flags.h

@@ -11,6 +11,7 @@
 namespace flags {
 
 extern const base::Feature kUnexpireFlagsM76;
+extern const base::Feature kUnexpireFlagsM78;
 
 bool IsFlagExpired(const char* internal_name);