Cleanup parameter passing issues in content/browser/download

content/browser/download/download_manager_impl.cc

Index: content/browser/download/download_manager_impl.cc
diff --git a/content/browser/download/download_manager_impl.cc b/content/browser/download/download_manager_impl.cc
index cb25d5fa8c35cce599c4de38af4c884a409ab536..5a7d97c29f02ad443833c1bb85a7a9151f2774bf 100644
--- a/content/browser/download/download_manager_impl.cc
+++ b/content/browser/download/download_manager_impl.cc
@@ -424,7 +424,7 @@ void DownloadManagerImpl::ContinueDownloadWithPath(
 void DownloadManagerImpl::UpdateDownload(int32 download_id,
                                          int64 bytes_so_far,
                                          int64 bytes_per_sec,
-                                         std::string hash_state) {
+                                         const std::string& hash_state) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   DownloadMap::iterator it = active_downloads_.find(download_id);
   if (it != active_downloads_.end()) {
@@ -623,7 +623,7 @@ void DownloadManagerImpl::DownloadCancelled(DownloadItem* download) {
 
 void DownloadManagerImpl::OnDownloadInterrupted(int32 download_id,
                                                 int64 size,
-                                                std::string hash_state,
+                                                const std::string& hash_state,
                                                 InterruptReason reason) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));