Reland "Remove BlockThirdPartyCookies preference"

This is a reland of 1180542b

The internal CL is rolled in now. Let's try again...

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: engedy@chromium.org, gab@chromium.org
Bug: 1104836, 1124326
Change-Id: Iebe3205beb4426cda5305eb7c69eb4e575df2cfc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2391073Reviewed-by: Christian Dullweber <dullweber@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Reviewed-by: Balazs Engedy <engedy@chromium.org>
Commit-Queue: Christian Dullweber <dullweber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804298}

chrome/browser/prefs/browser_prefs.cc

@@ -567,6 +567,9 @@ 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) {
@@ -675,6 +678,8 @@ void RegisterProfilePrefsForMigration(
   registry->RegisterDictionaryPref(kHashedAvailablePages);
 
   registry->RegisterDictionaryPref(kObservedSessionTime);
+
+  registry->RegisterBooleanPref(kBlockThirdPartyCookies, false);
 }
 
 }  // namespace
@@ -1341,4 +1346,7 @@ 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

@@ -60,9 +60,6 @@ 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),
@@ -240,7 +237,9 @@ void CookieSettings::GetCookieSettingInternal(
 
 CookieSettings::~CookieSettings() = default;
 
-bool CookieSettings::IsCookieControlsEnabled() {
+bool CookieSettings::ShouldBlockThirdPartyCookiesInternal() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
 #if defined(OS_IOS)
   if (!base::FeatureList::IsEnabled(kImprovedCookieControls))
     return false;
@@ -274,8 +273,7 @@ void CookieSettings::OnContentSettingChanged(
 void CookieSettings::OnCookiePreferencesChanged() {
   DCHECK(thread_checker_.CalledOnValidThread());
 
-  bool new_block_third_party_cookies =
-      IsCookieControlsEnabled();
+  bool new_block_third_party_cookies = ShouldBlockThirdPartyCookiesInternal();
 
   // 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

@@ -140,9 +140,6 @@ 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;
@@ -173,6 +170,10 @@ 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

@@ -6,10 +6,6 @@
 
 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

@@ -13,9 +13,6 @@ 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[];