Cleanup parameter passing issues in content/browser/download

content/public/browser/download_manager.h

Index: content/public/browser/download_manager.h
diff --git a/content/public/browser/download_manager.h b/content/public/browser/download_manager.h
index c123cc05a6d3d61528c419a8fc4896558f7c98e8..ef948b94e86d4d03ec294c2f15db1a178d3d6a7d 100644
--- a/content/public/browser/download_manager.h
+++ b/content/public/browser/download_manager.h
@@ -108,7 +108,7 @@ class CONTENT_EXPORT DownloadManager
   virtual void UpdateDownload(int32 download_id,
                               int64 bytes_so_far,
                               int64 bytes_per_sec,
-                              std::string hash_state) = 0;
+                              const std::string& hash_state) = 0;
 
   // |download_id| is the ID of the download.
   // |size| is the number of bytes that have been downloaded.
@@ -129,7 +129,7 @@ class CONTENT_EXPORT DownloadManager
   // |reason| is a download interrupt reason code.
   virtual void OnDownloadInterrupted(int32 download_id,
                                      int64 size,
-                                     std::string hash_state,
+                                     const std::string& hash_state,
                                      InterruptReason reason) = 0;
 
   // Called when the download is renamed to its final name.