Store per-origin metadata for localstorage.

content/browser/dom_storage/local_storage_database.proto

Index: content/browser/dom_storage/local_storage_database.proto
diff --git a/content/browser/dom_storage/local_storage_database.proto b/content/browser/dom_storage/local_storage_database.proto
new file mode 100644
index 0000000000000000000000000000000000000000..057308dbc292c54ab6a2f1c95ca521c9cc49eba9
--- /dev/null
+++ b/content/browser/dom_storage/local_storage_database.proto
@@ -0,0 +1,15 @@
+// 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.
+
+syntax = "proto2";
+
+option optimize_for = LITE_RUNTIME;
+
+package content;
+
+message LocalStorageOriginMetaData {
+  // Serialized by base::Time::ToInternalValue().
+  required int64 last_modified = 1;
+  required uint64 size_bytes = 2;
+}