[Offline Pages] Download UI: Remove all observers when clearing cache.

components/offline_pages/core/downloads/download_ui_adapter_unittest.cc

 // Copyright 2016 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.
 
 #include "components/offline_pages/core/downloads/download_ui_adapter.h"
 
 #include <stdint.h>
 
 #include <map>
 #include <memory>
@@ skipping 421 matching lines @@
   EXPECT_EQ(0UL, added_guids.size());
   EXPECT_EQ(0UL, deleted_guids.size());
 
   EXPECT_GE(updated_guids.size(), 1UL);
   std::string last_updated_guid = updated_guids[updated_guids.size() - 1];
   item = adapter->GetItem(last_updated_guid);
   EXPECT_NE(nullptr, item);
   EXPECT_EQ(DownloadUIItem::DownloadState::COMPLETE, item->download_state);
 }
 
+TEST_F(DownloadUIAdapterTest, RemoveObserversWhenClearingCache) {
+  PumpLoop();
+  EXPECT_TRUE(items_loaded);
+
+  // Remove this from the adapter's observer list.  This should cause the cache
+  // to be cleared.
+  adapter->RemoveObserver(this);
+  items_loaded = false;
+
+  PumpLoop();
+
+  adapter->AddObserver(this);
+  PumpLoop();
+  EXPECT_TRUE(items_loaded);
+}
+
 }  // namespace offline_pages