Refactor how the updater state data is serialized in update checks.

components/update_client/BUILD.gn

Index: components/update_client/BUILD.gn
diff --git a/components/update_client/BUILD.gn b/components/update_client/BUILD.gn
index 4b8548fcbfb35d07953fdab1b6d3f3a2660ca3ee..7e0164f1fb062d7706e51c80bff7f3aff22c478d 100644
--- a/components/update_client/BUILD.gn
+++ b/components/update_client/BUILD.gn
@@ -49,6 +49,9 @@ static_library("update_client") {
     "update_query_params_delegate.h",
     "update_response.cc",
     "update_response.h",
+    "updater_state.cc",
+    "updater_state.h",
+    "updater_state_win.cc",
     "url_fetcher_downloader.cc",
     "url_fetcher_downloader.h",
     "utils.cc",
@@ -126,6 +129,7 @@ source_set("unit_tests") {
     "update_client_unittest.cc",
     "update_query_params_unittest.cc",
     "update_response_unittest.cc",
+    "updater_state_unittest.cc",
     "utils_unittest.cc",
   ]