content: Cleanup class/struct forward declarations

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 7b04179b03be24f6b87de5650f194cd6bdf616ad..a4a5134a9c819f44d0045314d096688716d5b856 100644
--- a/content/public/browser/download_manager.h
+++ b/content/public/browser/download_manager.h
@@ -43,17 +43,11 @@
 
 class GURL;
 
-namespace url {
-class Origin;
-}
-
 namespace content {
 
 class BrowserContext;
 class ByteStreamReader;
 class DownloadManagerDelegate;
-class DownloadQuery;
-class DownloadRequestHandle;
 struct DownloadCreateInfo;
 
 // Browser's download manager: manages all downloads and destination view.