downloads: add the ability to undo download removal.

chrome/browser/download/download_history.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // DownloadHistory manages persisting DownloadItems to the history service by
 // observing a single DownloadManager and all its DownloadItems using an
 // AllDownloadItemNotifier.
 //
 // DownloadHistory decides whether and when to add items to, remove items from,
 // and update items in the database. DownloadHistory uses DownloadHistoryData to
@@ skipping 53 matching lines @@
   }
 
   static const DownloadHistoryData* Get(const content::DownloadItem* item) {
     const base::SupportsUserData::Data* data = item->GetUserData(kKey);
     return (data == NULL) ? NULL
                           : static_cast<const DownloadHistoryData*>(data);
   }
 
   explicit DownloadHistoryData(content::DownloadItem* item)
       : state_(NOT_PERSISTED),
-        was_restored_from_history_(false) {
+        was_restored_from_history_(false),
+        was_revived_(false) {
     item->SetUserData(kKey, this);
   }
 
   ~DownloadHistoryData() override {}
 
   PersistenceState state() const { return state_; }
   void SetState(PersistenceState s) { state_ = s; }
 
   bool was_restored_from_history() const { return was_restored_from_history_; }
   void set_was_restored_from_history(bool value) {
     was_restored_from_history_ = value;
   }
 
+  bool was_revived() const { return was_revived_; }
+  void set_was_revived(bool revived) { was_revived_ = revived; }
+
   // This allows DownloadHistory::OnDownloadUpdated() to see what changed in a
   // DownloadItem if anything, in order to prevent writing to the database
   // unnecessarily.  It is nullified when the item is no longer in progress in
   // order to save memory.
   history::DownloadRow* info() { return info_.get(); }
   void set_info(const history::DownloadRow& i) {
     info_.reset(new history::DownloadRow(i));
   }
   void clear_info() {
     info_.reset();
   }
 
  private:
   static const char kKey[];
 
   PersistenceState state_;
   scoped_ptr<history::DownloadRow> info_;
   bool was_restored_from_history_;
+  bool was_revived_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadHistoryData);
 };
 
 const char DownloadHistoryData::kKey[] =
   "DownloadItem DownloadHistoryData";
 
 history::DownloadRow GetDownloadRow(
     content::DownloadItem* item) {
   std::string by_ext_id, by_ext_name;
@@ skipping 249 matching lines @@
   // observer that can also see data->state(), which is the only thing that
   // ItemAdded() changed.
   OnDownloadUpdated(notifier_.GetManager(), item);
 }
 
 void DownloadHistory::OnDownloadCreated(
     content::DownloadManager* manager, content::DownloadItem* item) {
   DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
 
   // All downloads should pass through OnDownloadCreated exactly once.
-  CHECK(!DownloadHistoryData::Get(item));
-  DownloadHistoryData* data = new DownloadHistoryData(item);
+  DownloadHistoryData* data = DownloadHistoryData::Get(item);
+  CHECK(!data || data->was_revived());
+
+  if (!data)
+    data = new DownloadHistoryData(item);
+
   if (item->GetId() == loading_id_) {
     data->SetState(DownloadHistoryData::PERSISTED);
     data->set_was_restored_from_history(true);
     loading_id_ = content::DownloadItem::kInvalidId;
   }
   if (item->GetState() == content::DownloadItem::IN_PROGRESS) {
     data->set_info(GetDownloadRow(item));
   }
   MaybeAddToHistory(item);
 }
 
+void DownloadHistory::OnDownloadRevived(
+    content::DownloadManager* manager, content::DownloadItem* item) {
+  DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
+
+  DownloadHistoryData* data = DownloadHistoryData::Get(item);
+  if (data)
+    data->set_was_revived(true);
+}
+
 void DownloadHistory::OnDownloadUpdated(
     content::DownloadManager* manager, content::DownloadItem* item) {
   DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
 
   DownloadHistoryData* data = DownloadHistoryData::Get(item);
   if (data->state() == DownloadHistoryData::NOT_PERSISTED) {
     MaybeAddToHistory(item);
     return;
   }
   if (item->IsTemporary()) {
@@ skipping 57 matching lines @@
   removing_ids_.insert(download_id);
 }
 
 void DownloadHistory::RemoveDownloadsBatch() {
   DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
   IdSet remove_ids;
   removing_ids_.swap(remove_ids);
   history_->RemoveDownloads(remove_ids);
   FOR_EACH_OBSERVER(Observer, observers_, OnDownloadsRemoved(remove_ids));
 }