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

chrome/browser/download/trusted_sources_manager.h

Index: chrome/browser/download/trusted_sources_manager.h
diff --git a/chrome/browser/download/trusted_sources_manager.h b/chrome/browser/download/trusted_sources_manager.h
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+++ b/chrome/browser/download/trusted_sources_manager.h
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+// 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.
+
+#ifndef CHROME_BROWSER_DOWNLOAD_TRUSTED_SOURCES_MANAGER_H_
+#define CHROME_BROWSER_DOWNLOAD_TRUSTED_SOURCES_MANAGER_H_
+
+#include "base/macros.h"
+#include "net/proxy/proxy_bypass_rules.h"
+
+class GURL;
+
+// Identifies if a URL is from a trusted source.
+class TrustedSourcesManager {
+ public:
+  virtual ~TrustedSourcesManager();
+
+  // Creates a platform-dependent instance of TrustedSourcesManager.
+  //
+  // A trusted sources manager has a list of sources that can be trusted with
+  // downloads, extracted from the kTrustedDownloadSources command line switch.
+  // An example usage is to specify that files downloaded from trusted sites
+  // don't need to be scanned by SafeBrowsing when the
+  // SafeBrowsingForTrustedSourcesEnabled policy is set to false.
+  //
+  // On creation the list of trusted sources is NULL.
+  //
+  // If the platform is Windows, on top of the kTrustedDownloadSources value,
+  // the security zone mapping is used to determine whether the source is
+  // trusted or not.
+  //
+  static TrustedSourcesManager* Create();
+
+  // Returns true if the source of this URL is part of the trusted sources.
+  virtual bool IsFromTrustedSource(const GURL& url) const;
+
+ protected:
+  // Must use Create.
+  TrustedSourcesManager();
+
+ private:
+  // We are using ProxyBypassRules because they have the functionality that we
+  // want, but we are not using it for proxy bypass.
+  net::ProxyBypassRules rules_;
+
+  DISALLOW_COPY_AND_ASSIGN(TrustedSourcesManager);
+};
+
+#endif  // CHROME_BROWSER_DOWNLOAD_TRUSTED_SOURCES_MANAGER_H_