Revert "Reland "Remove BlockThirdPartyCookies preference""

This reverts commit e8bb886c.

Reason for revert: Still breaks perf bots: crbug/1124326

Original change's description:
> Reland "Remove BlockThirdPartyCookies preference"
> 
> This is a reland of 1180542b
> 
> BLOCK_THIRD_PARTY_COOKIES usage in clank is fixed:
> https://crrev.com/i/3250184
> 
> Original change's description:
> > Remove BlockThirdPartyCookies preference
> >
> > The boolean BlockThirdPartyCookies preference was replaced by
> > CookieControlsMode enum. Existing settings were migrated since M83.
> > Since all usage of the preference has been removed, the preference
> > can be removed and existing settings cleared.
> >
> > Bug: 1104836
> > Change-Id: Ie6e38b0a424981395c627459d684030ea84a58b7
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2387805
> > Reviewed-by: Balazs Engedy <engedy@chromium.org>
> > Reviewed-by: Gabriel Charette <gab@chromium.org>
> > Commit-Queue: Christian Dullweber <dullweber@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#803844}
> 
> Tbr: gab@chromium.org
> Bug: 1104836
> Change-Id: If89041daa0a46da604171acf734b9733d9a24e07
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2390655
> Commit-Queue: Christian Dullweber <dullweber@chromium.org>
> Reviewed-by: Balazs Engedy <engedy@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#804217}

TBR=gab@chromium.org,engedy@chromium.org,dullweber@chromium.org

Change-Id: I2a6799c01373c1b5b265fa2518406a2305e1dbd7
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1104836,1124326
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2390912Reviewed-by: Stephen Nusko <nuskos@chromium.org>
Commit-Queue: Stephen Nusko <nuskos@chromium.org>
Auto-Submit: Stephen Nusko <nuskos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804224}

chrome/browser/prefs/browser_prefs.cc

@@ -567,9 +567,6 @@ const char kHashedAvailablePages[] = "previews.offline_helper.available_pages";
 // Deprecated 7/2020
 const char kObservedSessionTime[] = "profile.observed_session_time";
 
-// Deprecated 9/2020
-const char kBlockThirdPartyCookies[] = "profile.block_third_party_cookies";
-
 // Register local state used only for migration (clearing or moving to a new
 // key).
 void RegisterLocalStatePrefsForMigration(PrefRegistrySimple* registry) {
@@ -678,8 +675,6 @@ void RegisterProfilePrefsForMigration(
   registry->RegisterDictionaryPref(kHashedAvailablePages);
 
   registry->RegisterDictionaryPref(kObservedSessionTime);
-
-  registry->RegisterBooleanPref(kBlockThirdPartyCookies, false);
 }
 
 }  // namespace
@@ -1346,7 +1341,4 @@ void MigrateObsoleteProfilePrefs(Profile* profile) {
 
   // Added 7/2020
   profile_prefs->ClearPref(kObservedSessionTime);
-
-  // Added 9/2020
-  profile_prefs->ClearPref(kBlockThirdPartyCookies);
 }

components/content_settings/core/browser/cookie_settings.cc

@@ -60,6 +60,9 @@ void CookieSettings::GetCookieSettings(
 
 void CookieSettings::RegisterProfilePrefs(
     user_prefs::PrefRegistrySyncable* registry) {
+  registry->RegisterBooleanPref(
+      prefs::kBlockThirdPartyCookies, false,
+      user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
   registry->RegisterIntegerPref(
       prefs::kCookieControlsMode,
       static_cast<int>(CookieControlsMode::kIncognitoOnly),
@@ -237,9 +240,7 @@ void CookieSettings::GetCookieSettingInternal(
 
 CookieSettings::~CookieSettings() = default;
 
-bool CookieSettings::ShouldBlockThirdPartyCookiesInternal() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-
+bool CookieSettings::IsCookieControlsEnabled() {
 #if defined(OS_IOS)
   if (!base::FeatureList::IsEnabled(kImprovedCookieControls))
     return false;
@@ -273,7 +274,8 @@ void CookieSettings::OnContentSettingChanged(
 void CookieSettings::OnCookiePreferencesChanged() {
   DCHECK(thread_checker_.CalledOnValidThread());
 
-  bool new_block_third_party_cookies = ShouldBlockThirdPartyCookiesInternal();
+  bool new_block_third_party_cookies =
+      IsCookieControlsEnabled();
 
   // Safe to read |block_third_party_cookies_| without locking here because the
   // only place that writes to it is this method and it will always be run on

components/content_settings/core/browser/cookie_settings.h

@@ -140,6 +140,9 @@ class CookieSettings : public CookieSettingsBase,
 
   void RemoveObserver(Observer* obs) { observers_.RemoveObserver(obs); }
 
+  // Returns true when the improved cookie control UI should be shown.
+  // TODO(dullweber): Fix grammar.
+  bool IsCookieControlsEnabled();
 
  private:
   ~CookieSettings() override;
@@ -170,10 +173,6 @@ class CookieSettings : public CookieSettingsBase,
 
   void OnCookiePreferencesChanged();
 
-  // Evaluate if third-party cookies are blocked. Should only be called
-  // when the preference changes to update the internal state.
-  bool ShouldBlockThirdPartyCookiesInternal();
-
   base::ThreadChecker thread_checker_;
   base::ObserverList<Observer> observers_;
   scoped_refptr<HostContentSettingsMap> host_content_settings_map_;

components/content_settings/core/common/pref_names.cc

@@ -6,6 +6,10 @@
 
 namespace prefs {
 
+// Boolean that is true if we should unconditionally block third-party cookies,
+// regardless of other content settings.
+const char kBlockThirdPartyCookies[] = "profile.block_third_party_cookies";
+
 // CookieControlsMode enum value that decides when the cookie controls UI is
 // enabled. This will block third-party cookies similar to
 // kBlockThirdPartyCookies but with a new UI.

components/content_settings/core/common/pref_names.h

@@ -13,6 +13,9 @@ namespace prefs {
 // some of these are generated by WebsiteSettingsInfo from content settings
 // names.
 
+// TODO(crbug.com/967668): Remove direct access to these preferences and
+// replace with CookieSettings::ShouldBlockThirdPartyCookies().
+extern const char kBlockThirdPartyCookies[];
 extern const char kCookieControlsMode[];
 
 extern const char kContentSettingsVersion[];