Wire up download attribution enable finch experiment

chrome/browser/safe_browsing/download_protection_service.h

Index: chrome/browser/safe_browsing/download_protection_service.h
diff --git a/chrome/browser/safe_browsing/download_protection_service.h b/chrome/browser/safe_browsing/download_protection_service.h
index fbe44d810624941254ed9f45df68b39a492e92f6..213e2a7443eecf4c0ca144ecd003b68c8b9d7564 100644
--- a/chrome/browser/safe_browsing/download_protection_service.h
+++ b/chrome/browser/safe_browsing/download_protection_service.h
@@ -23,6 +23,7 @@
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/supports_user_data.h"
+#include "chrome/browser/safe_browsing/safe_browsing_navigation_observer_manager.h"
 #include "chrome/browser/safe_browsing/ui_manager.h"
 #include "components/safe_browsing_db/database_manager.h"
 #include "net/url_request/url_request_context_getter.h"
@@ -287,9 +288,19 @@ class DownloadProtectionService {
   // Returns the URL that will be used for download requests.
   static GURL GetDownloadRequestUrl();
 
+  // If kDownloadAttribution feature is enabled, identify and add referrer chain
+  // info of a download to ClientDownloadRequest proto. This function also
+  // records UMA stats of download attribution result.
+  void AddReferrerChainToClientDownloadRequest(
+    const GURL& download_url,
+    content::WebContents* web_contents,
+    ClientDownloadRequest* out_request);
+
   // These pointers may be NULL if SafeBrowsing is disabled.
   scoped_refptr<SafeBrowsingUIManager> ui_manager_;
   scoped_refptr<SafeBrowsingDatabaseManager> database_manager_;
+  scoped_refptr<SafeBrowsingNavigationObserverManager>
+  navigation_observer_manager_;
 
   // The context we use to issue network requests.
   scoped_refptr<net::URLRequestContextGetter> request_context_getter_;