Created a DownloadManager interface, for use in unit tests..

content/browser/download/download_file_manager.h

Index: content/browser/download/download_file_manager.h
diff --git a/content/browser/download/download_file_manager.h b/content/browser/download/download_file_manager.h
index bf6e07beed78c91c2d7e7215b2e970b8ffd8c20d..78fe507facafbf5b88d2c54affcfa96bbaca9b8a 100644
--- a/content/browser/download/download_file_manager.h
+++ b/content/browser/download/download_file_manager.h
@@ -57,7 +57,7 @@
 struct DownloadCreateInfo;
 struct DownloadSaveInfo;
 class DownloadFile;
-class DownloadManager;
+class DownloadManagerInterface;
 class DownloadRequestHandle;
 class FilePath;
 class GURL;
@@ -106,7 +106,7 @@ class CONTENT_EXPORT DownloadFileManager
   void CompleteDownload(DownloadId id);
 
   // Called on FILE thread by DownloadManager at the beginning of its shutdown.
-  void OnDownloadManagerShutdown(DownloadManager* manager);
+  void OnDownloadManagerShutdown(DownloadManagerInterface* manager);
 
   // The DownloadManager in the UI thread has provided an intermediate
   // .crdownload name for the download specified by |id|.
@@ -146,7 +146,7 @@ class CONTENT_EXPORT DownloadFileManager
   // process.
   void CreateDownloadFile(DownloadCreateInfo* info,
                           const DownloadRequestHandle& request_handle,
-                          DownloadManager* download_manager,
+                          DownloadManagerInterface* download_manager,
                           bool hash_needed);
 
   // Called only on the download thread.