[Downloads] Rework how hashes are calculated for download files.

chrome/browser/download/download_history.cc

Index: chrome/browser/download/download_history.cc
diff --git a/chrome/browser/download/download_history.cc b/chrome/browser/download/download_history.cc
index b901ce4e40c5c691dbeba374bef1e397ba1891ee..12f0b9ea6011adbf40b5a1f8487e95e0665bdf59 100644
--- a/chrome/browser/download/download_history.cc
+++ b/chrome/browser/download/download_history.cc
@@ -264,19 +264,13 @@ void DownloadHistory::QueryCallback(scoped_ptr<InfoVector> infos) {
        it != infos->end(); ++it) {
     loading_id_ = history::ToContentDownloadId(it->id);
     content::DownloadItem* item = notifier_.GetManager()->CreateDownloadItem(
-        loading_id_,
-        it->current_path,
-        it->target_path,
-        it->url_chain,
-        it->referrer_url,
-        it->mime_type,
-        it->original_mime_type,
-        it->start_time,
-        it->end_time,
-        it->etag,
-        it->last_modified,
-        it->received_bytes,
+        loading_id_, it->current_path, it->target_path, it->url_chain,
+        it->referrer_url, it->mime_type, it->original_mime_type, it->start_time,
+        it->end_time, it->etag, it->last_modified, it->received_bytes,
         it->total_bytes,
+        std::string(),  // TODO(asanka): Need to persist and restore hash of
+                        // partial file for an interrupted download. No need to
+                        // store hash for a completed file.
         history::ToContentDownloadState(it->state),
         history::ToContentDownloadDangerType(it->danger_type),
         history::ToContentDownloadInterruptReason(it->interrupt_reason),