[Downloads] Use the initiating StoragePartition for resumption.

content/browser/download/download_create_info.h

Index: content/browser/download/download_create_info.h
diff --git a/content/browser/download/download_create_info.h b/content/browser/download/download_create_info.h
index 794b3c6e8c0805293eb5b8bc4c704602de89c94c..ead25417dbc82e81ff8ef51281fd79340dd1edb5 100644
--- a/content/browser/download/download_create_info.h
+++ b/content/browser/download/download_create_info.h
@@ -46,6 +46,9 @@ struct CONTENT_EXPORT DownloadCreateInfo {
   // The URL that referred us.
   GURL referrer_url;
 
+  // Site URL for the site instance that initiated the download.
+  GURL site_url;
+
   // The URL of the tab that started us.
   GURL tab_url;