Add a Restore() method to ValueStore and make StorageAPI use it

chrome/browser/extensions/api/storage/local_storage_backend.cc

+// Copyright 2014 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 "chrome/browser/extensions/api/storage/local_storage_backend.h"
+
+#include "base/file_util.h"
+#include "chrome/browser/extensions/api/storage/settings_storage_factory.h"
+
+namespace extensions {
+
+LocalStorageBackend::LocalStorageBackend(
+    const scoped_refptr<SettingsStorageFactory>& storage_factory,
+    const base::FilePath& base_path,
+    const SettingsStorageQuotaEnforcer::Limits& quota)
+    : SettingsBackend(storage_factory, base_path, quota) {}
+
+LocalStorageBackend::~LocalStorageBackend() {}
+
+ValueStore* LocalStorageBackend::GetStorage(const std::string& extension_id) {
+  StorageMap::iterator iter = storage_map_.find(extension_id);
+  if (iter != storage_map_.end())
+    return iter->second.get();
+
+  // Unlike SyncStorageBackend, we don't check for corruption at initialization.
+  // This is because a) we don't need to, since we'll catch it when we try to
+  // use it in an API call, and b) because local storage can be much larger
+  // than sync storage, resulting in a much more significant overhead.
+  linked_ptr<ValueStore> storage(new SettingsStorageQuotaEnforcer(
+      quota(), storage_factory()->Create(base_path(), extension_id)));
+
+  storage_map_[extension_id] = storage;
+  return storage.get();
+}
+
+void LocalStorageBackend::DeleteStorage(const std::string& extension_id) {
+  // Clear settings when the extension is uninstalled.  Leveldb implementations
+  // will also delete the database from disk when the object is destroyed as a
+  // result of being removed from |storage_map_|.
+  StorageMap::iterator iter = storage_map_.find(extension_id);
+  if (iter == storage_map_.end()) {
+    // If the key isn't in |storage_map_|, it's possible that the extension
+    // still has storage and that the storage area was just unloaded. Check if
+    // the path exists, and, if it does, load it in order to delete it.
+    if (base::PathExists(
+            storage_factory()->GetDatabasePath(base_path(), extension_id))) {
+      GetStorage(extension_id);

[not at google - send to devlin, 2014/02/14 19:35:56]

Creating a storage area here just to delete it straight away seems like
overkill. Can you just delete it on the file system directly?

[Devlin, 2014/02/18 23:55:22]

Initially, I thought there was more cleanup involved when we deleted a db. 
Apparently not.  Makes it much simpler.  Thanks :)

+    } else {
+      return;
+    }
+  }
+  storage_map_.erase(extension_id);
+}
+
+}  // namespace extensions