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

chrome/browser/download/chrome_download_manager_delegate.cc

Index: chrome/browser/download/chrome_download_manager_delegate.cc
diff --git a/chrome/browser/download/chrome_download_manager_delegate.cc b/chrome/browser/download/chrome_download_manager_delegate.cc
index 15e6f80f5774e1f4ca7dd9f33b26e375df960c3b..e6343383bd44cc1a2fcd12fe5d7b0430c3de38a1 100644
--- a/chrome/browser/download/chrome_download_manager_delegate.cc
+++ b/chrome/browser/download/chrome_download_manager_delegate.cc
@@ -340,6 +340,11 @@ bool ChromeDownloadManagerDelegate::IsDownloadReadyForCompletion(
     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) {