Add migration code to change existing domain scoped content settings to be origin scoped

components/content_settings/core/browser/host_content_settings_map.h

Index: components/content_settings/core/browser/host_content_settings_map.h
diff --git a/components/content_settings/core/browser/host_content_settings_map.h b/components/content_settings/core/browser/host_content_settings_map.h
index ec33722e9996e4b9250274a0746a06ce9b1f436b..9115c2836a932b70c52fada8c8d6c27a991f454e 100644
--- a/components/content_settings/core/browser/host_content_settings_map.h
+++ b/components/content_settings/core/browser/host_content_settings_map.h
@@ -280,6 +280,7 @@ class HostContentSettingsMap : public content_settings::Observer,
 
  private:
   friend class base::RefCountedThreadSafe<HostContentSettingsMap>;
+  friend class HostContentSettingsMapTest_MigrateDomainScopedSettings_Test;
   friend class HostContentSettingsMapTest_MigrateKeygenSettings_Test;
 
   friend class content_settings::TestUtils;
@@ -311,6 +312,14 @@ class HostContentSettingsMap : public content_settings::Observer,
   // leave in some code to remove old-format settings for a long time.
   void MigrateKeygenSettings();
 
+  // Migrate old domain scoped ALLOW settings to be origin scoped for
+  // ContentSettingsTypes which are domain scoped. Only narrow down ALLOW
+  // domain settings to origins so that this will not cause privacy/security
+  // issues.
+  // TODO(lshang): https://crbug.com/621398 Remove this when clients have
+  // migrated (~M56).
+  void MigrateDomainScopedSettings();
+
   // Collect UMA data about the number of exceptions.
   void RecordNumberOfExceptions();