downloads: add the ability to undo download removal.

chrome/browser/ui/webui/downloads_dom_handler.h

Index: chrome/browser/ui/webui/downloads_dom_handler.h
diff --git a/chrome/browser/ui/webui/downloads_dom_handler.h b/chrome/browser/ui/webui/downloads_dom_handler.h
index 30c42e387b37da8ced1c1b5c89791ee5f2586693..d40c164eb508271a0264681ec1825514adfd1076 100644
--- a/chrome/browser/ui/webui/downloads_dom_handler.h
+++ b/chrome/browser/ui/webui/downloads_dom_handler.h
@@ -88,6 +88,9 @@ class DownloadsDOMHandler : public content::WebUIMessageHandler,
   // folder.
   void HandleOpenDownloadsFolder(const base::ListValue* args);
 
+  // Callback for the "undoRemove" message. Undoes any previous removal.
+  void HandleUndoRemove(const base::ListValue* args);
+
  protected:
   // These methods are for mocking so that most of this class does not actually
   // depend on WebUI. The other methods that depend on WebUI are
@@ -124,6 +127,9 @@ class DownloadsDOMHandler : public content::WebUIMessageHandler,
   // to be deleted.
   bool IsDeletingHistoryAllowed();
 
+  // Finalizes any pending removal (if there is one).
+  void FinalizeRemoval();
+
   // Returns the download that is referred to in a given value.
   content::DownloadItem* GetDownloadByValue(const base::ListValue* args);
 
@@ -140,6 +146,10 @@ class DownloadsDOMHandler : public content::WebUIMessageHandler,
   // Whether a call to SendCurrentDownloads() is currently scheduled.
   bool update_scheduled_;
 
+  // The last download removed from this page. If no download has been removed
+  // or a download is revived, this will be DownloadItem::kInvalidId.
+  uint32 last_removed_id_;
+
   base::WeakPtrFactory<DownloadsDOMHandler> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadsDOMHandler);