Detect removed files and reflect the state in chrome://downloads and the download shelf

chrome/browser/download/download_manager.h

Index: chrome/browser/download/download_manager.h
diff --git a/chrome/browser/download/download_manager.h b/chrome/browser/download/download_manager.h
index 84b83990bdc9d8b103e2cf6de26f95b2a6239305..639f09963761abd7ceedb59028960794c8c8575b 100644
--- a/chrome/browser/download/download_manager.h
+++ b/chrome/browser/download/download_manager.h
@@ -233,6 +233,11 @@ class DownloadManager
   // Called when the user has validated the download of a dangerous file.
   void DangerousDownloadValidated(DownloadItem* download);
 
+  // Checks whether downloaded files still exist. Updates state of downloads
+  // that refer to removed files. The check runs in the background and may
+  // finish asynchronously after this method returns.
+  void CheckForFilesRemoval();
+
   // Callback function after url is checked with safebrowsing service.
   void CheckDownloadUrlDone(DownloadCreateInfo* info, bool is_dangerous_url);
 
@@ -272,6 +277,15 @@ class DownloadManager
 
   ~DownloadManager();
 
+  // Called on the FILE thread to check the existence of downloaded files.
+  void CheckForFilesRemovalOnFileThread(int64 db_handle, const FilePath& path);
+
+  // Called on the UI thread when the FILE thread finishes to check the
+  // existence of downloaded files. The UI thread updates the state of the
+  // downloaded but non-existent files, and then notifies the fact to the
+  // observers of those files.
+  void OnFilesRemovalDetected(int64 db_handle, bool file_exists);
+
   // Called on the download thread to check whether the suggested file path
   // exists.  We don't check if the file exists on the UI thread to avoid UI
   // stalls from interacting with the file system.