Add a new group policy to disable safe browsing for files downloaded from trusted sources.

chrome/browser/download/trusted_sources_manager_posix.cc

Index: chrome/browser/download/trusted_sources_manager_posix.cc
diff --git a/chrome/browser/download/trusted_sources_manager_posix.cc b/chrome/browser/download/trusted_sources_manager_posix.cc
new file mode 100644
index 0000000000000000000000000000000000000000..0c0adab4ad57e9a262ff883dab2bbc8ea90f695e
--- /dev/null
+++ b/chrome/browser/download/trusted_sources_manager_posix.cc
@@ -0,0 +1,10 @@
+// Copyright (c) 2017 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/browser/download/trusted_sources_manager.h"
+
+// static
+TrustedSourcesManager* TrustedSourcesManager::Create() {
+  return new TrustedSourcesManager;
+}