Make the UI an observer of downloads.

chrome/browser/extensions/extension_host.cc

Index: chrome/browser/extensions/extension_host.cc
diff --git a/chrome/browser/extensions/extension_host.cc b/chrome/browser/extensions/extension_host.cc
index 72bc8bc2e078e6f631399af39979a6ab685c158f..228120d9dfac0f033f905d53d6cffa7e29b8320b 100644
--- a/chrome/browser/extensions/extension_host.cc
+++ b/chrome/browser/extensions/extension_host.cc
@@ -414,16 +414,6 @@ void ExtensionHost::CloseContents(WebContents* contents) {
   }
 }
 
-void ExtensionHost::OnStartDownload(
-    content::WebContents* source, content::DownloadItem* download) {
-  // If |source| is in the context of a Browser, show the DownloadShelf on that
-  // Browser.
-  if (!view() || !view()->browser())
-    return;
-  static_cast<content::WebContentsDelegate*>(view()->browser())->
-    OnStartDownload(source, download);
-}
-
 void ExtensionHost::WebIntentDispatch(
     content::WebContents* web_contents,
     content::WebIntentsDispatcher* intents_dispatcher) {