Remove EmptyRuleIterators with nullptrs.

components/content_settings/core/browser/content_settings_provider.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Interface for objects providing content setting rules.
 
 #ifndef COMPONENTS_CONTENT_SETTINGS_CORE_BROWSER_CONTENT_SETTINGS_PROVIDER_H_
 #define COMPONENTS_CONTENT_SETTINGS_CORE_BROWSER_CONTENT_SETTINGS_PROVIDER_H_
 
 #include <memory>
@@ skipping 14 matching lines @@
  public:
   virtual ~ProviderInterface() {}
 
   // Returns a |RuleIterator| over the content setting rules stored by this
   // provider. If |incognito| is true, the iterator returns only the content
   // settings which are applicable to the incognito mode and differ from the
   // normal mode. Otherwise, it returns the content settings for the normal
   // mode. It is not allowed to call other |ProviderInterface| functions
   // (including |GetRuleIterator|) for the same provider until the
   // |RuleIterator| is destroyed.
+  // Returns nullptr to indicate the RuleIterator is empty.
   virtual std::unique_ptr<RuleIterator> GetRuleIterator(
       ContentSettingsType content_type,
       const ResourceIdentifier& resource_identifier,
       bool incognito) const = 0;
 
   // Asks the provider to set the website setting for a particular
   // |primary_pattern|, |secondary_pattern|, |content_type| tuple. If the
   // provider accepts the setting it returns true and takes the ownership of the
   // |value|. Otherwise false is returned and the ownership of the |value| stays
   // with the caller.
@@ skipping 18 matching lines @@
   // Detaches the Provider from all Profile-related objects like PrefService.
   // This methods needs to be called before destroying the Profile.
   // Afterwards, none of the methods above that should only be called on the UI
   // thread should be called anymore.
   virtual void ShutdownOnUIThread() = 0;
 };
 
 }  // namespace content_settings
 
 #endif  // COMPONENTS_CONTENT_SETTINGS_CORE_BROWSER_CONTENT_SETTINGS_PROVIDER_H_