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

chrome/browser/download/download_manager.cc

Index: chrome/browser/download/download_manager.cc
diff --git a/chrome/browser/download/download_manager.cc b/chrome/browser/download/download_manager.cc
index 6ef4a2b1e812ba36598d087e77f7925cacde2c3a..0a49ecb1883c30c10bdc818c13098826814c3679 100644
--- a/chrome/browser/download/download_manager.cc
+++ b/chrome/browser/download/download_manager.cc
@@ -265,6 +265,54 @@ void DownloadManager::StartDownload(DownloadCreateInfo* info) {
       info, NewCallback(this, &DownloadManager::CheckDownloadUrlDone));
 }
 
+void DownloadManager::CheckExistingPaths() {
+  PathVector existing_paths;
+  for (DownloadMap::iterator it = history_downloads_.begin();
+       it != history_downloads_.end(); ++it) {
+    DownloadItem* download_item = it->second;
+    if (download_item->IsComplete() && download_item->is_path_exists()) {
+      existing_paths.push_back(std::pair<int64, FilePath>(
+          it->first, download_item->GetTargetFilePath()));
+    }
+  }
+
+  BrowserThread::PostTask(
+      BrowserThread::FILE, FROM_HERE,
+      NewRunnableMethod(this,
+                        &DownloadManager::CheckExistingPathsOnFileThread,
+                        existing_paths));
+}
+
+void DownloadManager::CheckExistingPathsOnFileThread(
+    PathVector existing_paths) {
+  PathVector removed_paths;
+  for (PathVector::iterator it = existing_paths.begin();
+       it != existing_paths.end(); ++it) {
+    if (!file_util::PathExists(it->second)) {
+      removed_paths.push_back(std::pair<int64, FilePath>(
+          it->first, it->second));
+    }
+  }
+
+  BrowserThread::PostTask(
+      BrowserThread::UI, FROM_HERE,
+      NewRunnableMethod(this,
+                        &DownloadManager::OnExistingPathsAvailable,
+                        removed_paths));
+}
+
+void DownloadManager::OnExistingPathsAvailable(PathVector removed_paths) {
+  for (PathVector::iterator it = removed_paths.begin();
+       it != removed_paths.end(); ++it) {
+    DownloadMap::iterator map_it = history_downloads_.find(it->first);
+    if (map_it != history_downloads_.end()) {
+      DownloadItem* download_item = map_it->second;
+      download_item->set_is_path_exists(false);
+      download_item->UpdateObservers();
+    }
+  }
+}
+
 void DownloadManager::CheckDownloadUrlDone(DownloadCreateInfo* info,
                                            bool is_dangerous_url) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));