Content settings clean-up: Clarify resource identifier & get rid of NO_RESOURCE_IDENTIFIER.

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_
 
-#define NO_RESOURCE_IDENTIFIER std::string()
-
 #include <string>
 
 #include "base/values.h"
 #include "components/content_settings/core/common/content_settings_types.h"
 
 class ContentSettingsPattern;
 
 namespace content_settings {
 
 struct Rule;
@@ skipping 44 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_