chrome: Cleanup class/struct forward declarations

chrome/browser/profiles/profile_impl.h

 // Copyright (c) 2012 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.
 
 // This class gathers state related to a single user profile.
 
 #ifndef CHROME_BROWSER_PROFILES_PROFILE_IMPL_H_
 #define CHROME_BROWSER_PROFILES_PROFILE_IMPL_H_
 
 #include <memory>
@@ skipping 28 matching lines @@
 #endif
 
 namespace base {
 class SequencedTaskRunner;
 }
 
 namespace domain_reliability {
 class DomainReliabilityMonitor;
 }
 
-namespace extensions {
-class ExtensionSystem;
-}
-
 namespace policy {
 class CloudPolicyManager;
 class ProfilePolicyConnector;
 class SchemaRegistryService;
 }
 
 namespace ssl_config {
 class SSLConfigServiceManager;
 }
 
@@ skipping 207 matching lines @@
   // components/keyed_service/content/browser_context_keyed_service_factory.*
 
   Profile::Delegate* delegate_;
 
   chrome_browser_net::Predictor* predictor_;
 
   DISALLOW_COPY_AND_ASSIGN(ProfileImpl);
 };
 
 #endif  // CHROME_BROWSER_PROFILES_PROFILE_IMPL_H_