Allow fallback from https to http for component update checks.

components/component_updater/component_updater_url_constants.cc

Index: components/component_updater/component_updater_url_constants.cc
diff --git a/components/component_updater/component_updater_url_constants.cc b/components/component_updater/component_updater_url_constants.cc
index 3cb8ef1e289295f5bac947373088f0184385f1e9..c762cc91d9bef5ca0f0817f66887b68ccc4b1116 100644
--- a/components/component_updater/component_updater_url_constants.cc
+++ b/components/component_updater/component_updater_url_constants.cc
@@ -7,10 +7,15 @@
 namespace component_updater {
 
 // The default URL for the v3 protocol service endpoint. In some cases, the
-// component updater is allowed to fall back to and alternate URL source, if
+// component updater is allowed to fall back to other URL endpoints, if
 // the request to the default URL source fails.
+//
+// The responses to the requests made to these endpoints are always signed.
+//
 // The value of |kDefaultUrlSource| can be overridden with
 // --component-updater=url-source=someurl.
 const char kUpdaterDefaultUrl[] = "https://clients2.google.com/service/update2";
 
+const char kUpdaterFallbackUrl[] = "http://clients2.google.com/service/update2";
+
 }  // namespace component_updater