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

chrome/browser/extensions/api/storage/policy_value_store.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.
 
 #include "chrome/browser/extensions/api/storage/policy_value_store.h"
 
 #include "base/logging.h"
 #include "base/values.h"
 #include "chrome/browser/extensions/api/storage/settings_namespace.h"
 #include "chrome/browser/value_store/value_store_change.h"
@@ skipping 39 matching lines @@
           it->first, it->second.value->DeepCopy());
     }
   }
 
   // Get the previous policies stored in the database.
   // TODO(joaodasilva): it'd be better to have a less expensive way of
   // determining which keys are currently stored, or of determining which keys
   // must be removed.
   base::DictionaryValue previous_policy;
   ValueStore::ReadResult read_result = delegate_->Get();
+
+  // If the database is corrupted, try to restore it.
+  // This may have the unfortunate side-effect of incorrectly informing the
+  // extension of a "new" key, which isn't new and was corrupted. Unfortunately,
+  // there's not always a way around this - if the database is corrupted, there
+  // may be no way of telling which keys were previously present.
+  if (read_result->IsCorrupted()) {
+    if (delegate_->Restore())
+      read_result = delegate_->Get();
+  }
+
   if (read_result->HasError()) {
     LOG(WARNING) << "Failed to read managed settings for extension "
         << extension_id_ << ": " << read_result->error().message;
     // Leave |previous_policy| empty, so that events are generated for every
     // policy in |current_policy|.
   } else {
     read_result->settings().Swap(&previous_policy);
   }
 
   // Now get two lists of changes: changes after setting the current policies,
@@ skipping 84 matching lines @@
 
 ValueStore::WriteResult PolicyValueStore::Remove(
     const std::vector<std::string>& keys) {
   return MakeWriteResult(ReadOnlyError(util::NoKey()));
 }
 
 ValueStore::WriteResult PolicyValueStore::Clear() {
   return MakeWriteResult(ReadOnlyError(util::NoKey()));
 }
 
+bool PolicyValueStore::Restore() { return delegate_->Restore(); }
+
+bool PolicyValueStore::RestoreKey(const std::string& key) {
+  return delegate_->RestoreKey(key);
+}
+
 }  // namespace extensions