Revert of Enable Site Isolation for Extensions.

chrome/common/extensions/extension_process_policy.cc

 // 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.
 
 #include "chrome/common/extensions/extension_process_policy.h"
 
 #include "base/command_line.h"
 #include "base/metrics/field_trial.h"
 #include "base/strings/string_util.h"
 #include "chrome/common/extensions/extension_constants.h"
@@ skipping 50 matching lines @@
     if (old_url_is_hosted_app &&
         new_url_is_normal_or_hosted &&
         !either_is_web_store)
       return false;
   }
 
   return old_url_extension != new_url_extension;
 }
 
 bool IsIsolateExtensionsEnabled() {
-  return true;
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kIsolateExtensions)) {
+    return true;
+  }
+
+  const std::string group_name =
+      base::FieldTrialList::FindFullName("SiteIsolationExtensions");
+  // Use StartsWith() for more flexibility (e.g. multiple Enabled groups).
+  return base::StartsWith(group_name, "Enabled",
+                          base::CompareCase::INSENSITIVE_ASCII);
 }
 
 }  // namespace extensions