With --isolate-extensions, forking (via OpenURL) for extensions is not needed.

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/strings/string_util.h"
-#include "chrome/common/extensions/extension_constants.h"
-#include "extensions/common/constants.h"
-#include "extensions/common/extension.h"
-#include "extensions/common/extension_set.h"
-#include "extensions/common/manifest_handlers/app_isolation_info.h"
-#include "extensions/common/switches.h"
-
-namespace extensions {
-
-const extensions::Extension* GetNonBookmarkAppExtension(
-    const ExtensionSet& extensions, const GURL& url) {
-  // Exclude bookmark apps, which do not use the app process model.
-  const extensions::Extension* extension =
-      extensions.GetExtensionOrAppByURL(url);
-  if (extension && extension->from_bookmark())
-    extension = NULL;
-  return extension;
-}
-
-bool CrossesExtensionProcessBoundary(
-    const ExtensionSet& extensions,
-    const GURL& old_url,
-    const GURL& new_url,
-    bool should_consider_workaround) {
-  const extensions::Extension* old_url_extension = GetNonBookmarkAppExtension(
-      extensions,
-      old_url);
-  const extensions::Extension* new_url_extension = GetNonBookmarkAppExtension(
-      extensions,
-      new_url);
-
-  // TODO(creis): Temporary workaround for crbug.com/59285: Do not swap process
-  // to navigate from a hosted app to a normal page or another hosted app
-  // (unless either is the web store).  This is because some OAuth providers
-  // use non-app popups that communicate with non-app iframes inside the app
-  // (e.g., Facebook).  This would require out-of-process iframes to support.
-  // See http://crbug.com/99379.
-  // Note that we skip this exception for isolated apps, which require strict
-  // process separation from non-app pages.
-  if (should_consider_workaround) {
-    bool old_url_is_hosted_app = old_url_extension &&
-        !old_url_extension->web_extent().is_empty() &&
-        !AppIsolationInfo::HasIsolatedStorage(old_url_extension);
-    bool new_url_is_normal_or_hosted = !new_url_extension ||
-        (!new_url_extension->web_extent().is_empty() &&
-         !AppIsolationInfo::HasIsolatedStorage(new_url_extension));
-    bool either_is_web_store =
-        (old_url_extension &&
-        old_url_extension->id() == extensions::kWebStoreAppId) ||
-        (new_url_extension &&
-        new_url_extension->id() == extensions::kWebStoreAppId);
-    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;
-}
-
-}  // namespace extensions