Add the NotificationDatabaseData structure and protobuf

content/browser/notifications/BUILD.gn

Index: content/browser/notifications/BUILD.gn
diff --git a/chrome/browser/autocomplete/BUILD.gn b/content/browser/notifications/BUILD.gn
similarity index 58%
copy from chrome/browser/autocomplete/BUILD.gn
copy to content/browser/notifications/BUILD.gn
index 3f092810bdcbbf5b225bed5c7dfdf5a090bad7b1..0f6d5456988125873ebb894c8b61fe8383f46111 100644
--- a/chrome/browser/autocomplete/BUILD.gn
+++ b/content/browser/notifications/BUILD.gn
@@ -4,9 +4,8 @@
 
 import("//third_party/protobuf/proto_library.gni")
 
-# GYP version: chrome/chrome_browser.gypi:in_memory_url_index_cache_proto
-proto_library("in_memory_url_index_cache_proto") {
+proto_library("notification_proto") {
   sources = [
-    "in_memory_url_index_cache.proto",
+    "notification_database_data.proto",
   ]
 }