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

chrome/browser/download/chrome_download_manager_delegate.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/browser/download/chrome_download_manager_delegate.h"
 
 #include <string>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 322 matching lines @@
   }
   state->CompleteDownload();
 #endif
 }
 
 bool ChromeDownloadManagerDelegate::IsDownloadReadyForCompletion(
     DownloadItem* item,
     const base::Closure& internal_complete_callback) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 #if defined(FULL_SAFE_BROWSING)
+  if (!download_prefs_->safebrowsing_for_trusted_sources_enabled() &&
+      download_prefs_->IsFromTrustedSource(*item)) {
+    return true;
+  }
+
   SafeBrowsingState* state = static_cast<SafeBrowsingState*>(
       item->GetUserData(&kSafeBrowsingUserDataKey));
   if (!state) {
     // Begin the safe browsing download protection check.
     DownloadProtectionService* service = GetDownloadProtectionService();
     if (service) {
       DVLOG(2) << __func__ << "() Start SB download check for download = "
                << item->DebugString(false);
       state = new SafeBrowsingState();
       state->set_callback(internal_complete_callback);
@@ skipping 570 matching lines @@
 
     case (DownloadPrefs::DownloadRestriction::ALL_FILES):
       return true;
 
     default:
       LOG(ERROR) << "Invalid download restruction value: "
                  << static_cast<int>(download_restriction);
   }
   return false;
 }