Move enable extensions define to a build flag.

chrome/browser/autocomplete/keyword_extensions_delegate_impl.h

 // Copyright 2014 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.
 //
 // KeywordExtensionsDelegateImpl contains the extensions-only logic used by
 // KeywordProvider. Overrides KeywordExtensionsDelegate which does nothing.
 
 #ifndef CHROME_BROWSER_AUTOCOMPLETE_KEYWORD_EXTENSIONS_DELEGATE_IMPL_H_
 #define CHROME_BROWSER_AUTOCOMPLETE_KEYWORD_EXTENSIONS_DELEGATE_IMPL_H_
 
 #include <vector>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "components/omnibox/browser/autocomplete_input.h"
 #include "components/omnibox/browser/autocomplete_match.h"
 #include "components/omnibox/browser/autocomplete_provider_listener.h"
 #include "components/omnibox/browser/keyword_extensions_delegate.h"
 #include "components/omnibox/browser/keyword_provider.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
+#include "extensions/features/features.h"
 
-#if !defined(ENABLE_EXTENSIONS)
+#if !BUILDFLAG(ENABLE_EXTENSIONS)
 #error "Should not be included when extensions are disabled"
 #endif
 
 class Profile;
 
 class KeywordExtensionsDelegateImpl : public KeywordExtensionsDelegate,
                                       public content::NotificationObserver {
  public:
   KeywordExtensionsDelegateImpl(Profile* profile, KeywordProvider* provider);
   ~KeywordExtensionsDelegateImpl() override;
@@ skipping 47 matching lines @@
   content::NotificationRegistrar registrar_;
 
   // We need our input IDs to be unique across all profiles, so we keep a global
   // UID that each provider uses.
   static int global_input_uid_;
 
   DISALLOW_COPY_AND_ASSIGN(KeywordExtensionsDelegateImpl);
 };
 
 #endif  // CHROME_BROWSER_AUTOCOMPLETE_KEYWORD_EXTENSIONS_DELEGATE_IMPL_H_