Remove command line/field trial support and configs for Isolate Extensions.

chrome/common/extensions/extension_process_policy.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.
 
 #ifndef CHROME_COMMON_EXTENSIONS_EXTENSION_PROCESS_POLICY_H_
 #define CHROME_COMMON_EXTENSIONS_EXTENSION_PROCESS_POLICY_H_
 
 class GURL;
 
 namespace extensions {
@@ skipping 11 matching lines @@
 // extension URL).
 // We temporarily consider a workaround where we will keep non-app URLs in
 // an app process, but only if |should_consider_workaround| is true.  See
 // http://crbug.com/59285.
 bool CrossesExtensionProcessBoundary(
     const ExtensionSet& extensions,
     const GURL& old_url,
     const GURL& new_url,
     bool should_consider_workaround);
 
-// Check if extensions are running in Site Isolation mode.
-bool IsIsolateExtensionsEnabled();
-
 }  // namespace extensions
 
 #endif  // CHROME_COMMON_EXTENSIONS_EXTENSION_PROCESS_POLICY_H_