Deprecate the local browser preference for stacked tabs.

This preference is already ignored (assuming the default-enabled
force-disable-stacked-tabs flag is enabled), so this CL is a
behavioral no-op.

Bug: 1250061
Change-Id: I714406de6de740da58f053d313cfa650b0c8b996
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3206542
Reviewed-by: Dominic Battré <[email protected]>
Reviewed-by: Peter Boström <[email protected]>
Reviewed-by: David Pennington <[email protected]>
Commit-Queue: Taylor Bergquist <[email protected]>
Cr-Commit-Position: refs/heads/main@{#938043}
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index 05044d9..5a09b11 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -448,6 +448,8 @@
 #endif  // BUILDFLAG(ENABLE_SIDE_SEARCH)
 
 namespace {
+// Deprecated 10/2021
+const char kTabStripStackedLayout[] = "tab-strip-stacked-layout";
 
 #if BUILDFLAG(IS_CHROMEOS_ASH)
 // Deprecated 5/2021
@@ -690,6 +692,8 @@
 // Register local state used only for migration (clearing or moving to a new
 // key).
 void RegisterLocalStatePrefsForMigration(PrefRegistrySimple* registry) {
+  registry->RegisterBooleanPref(kTabStripStackedLayout, false);
+
 #if BUILDFLAG(IS_CHROMEOS_ASH)
   registry->RegisterDictionaryPref(kRegisteredSupervisedUserAllowlists);
   registry->RegisterStringPref(kFirstRunTrialGroup, std::string());
@@ -1118,10 +1122,6 @@
   DeviceOAuth2TokenStoreDesktop::RegisterPrefs(registry);
 #endif
 
-#if defined(TOOLKIT_VIEWS)
-  RegisterBrowserViewLocalPrefs(registry);
-#endif
-
   // This is intentionally last.
   RegisterLocalStatePrefsForMigration(registry);
 }
@@ -1525,6 +1525,9 @@
   // Added 09/2021.
   local_state->ClearPref(kCloudPolicyOverridesPlatformPolicy);
 
+  // Added 10/2021.
+  local_state->ClearPref(kTabStripStackedLayout);
+
   // Please don't delete the following line. It is used by PRESUBMIT.py.
   // END_MIGRATE_OBSOLETE_LOCAL_STATE_PREFS
 }