Added Aura notification that relaunch and powerwash is required in case of downgrade.

chromeos/dbus/update_engine_client.cc

Index: chromeos/dbus/update_engine_client.cc
diff --git a/chromeos/dbus/update_engine_client.cc b/chromeos/dbus/update_engine_client.cc
index f1866f5cfb99a0acf9c36d9b968553bc56aecd9d..11c204fa4634968ac3aacf8d27891aab3018b35d 100644
--- a/chromeos/dbus/update_engine_client.cc
+++ b/chromeos/dbus/update_engine_client.cc
@@ -18,11 +18,24 @@
 
 namespace chromeos {
 
+const std::string UpdateEngineClient::kReleaseChannelDev = "dev-channel";
+const std::string UpdateEngineClient::kReleaseChannelBeta = "beta-channel";
+const std::string UpdateEngineClient::kReleaseChannelStable = "stable-channel";
+
 namespace {
 
-const char kReleaseChannelDev[] = "dev-channel";
-const char kReleaseChannelBeta[] = "beta-channel";
-const char kReleaseChannelStable[] = "stable-channel";
+const std::string kRawReleaseChannelsList[] = {
+    UpdateEngineClient::kReleaseChannelDev,
+    UpdateEngineClient::kReleaseChannelBeta,
+    UpdateEngineClient::kReleaseChannelStable};
+
+}  // namespace
+
+const std::vector<std::string> UpdateEngineClient::kReleaseChannelsList(
+    kRawReleaseChannelsList,
+    kRawReleaseChannelsList + arraysize(kRawReleaseChannelsList));
+
+namespace {
 
 // Delay between successive state transitions during AU.
 const int kStateTransitionDefaultDelayMs = 3000;
@@ -66,9 +79,9 @@ void EmptyUpdateCheckCallbackBody(
 }
 
 bool IsValidChannel(const std::string& channel) {
-  return channel == kReleaseChannelDev ||
-      channel == kReleaseChannelBeta ||
-      channel == kReleaseChannelStable;
+  return channel == UpdateEngineClient::kReleaseChannelDev ||
+         channel == UpdateEngineClient::kReleaseChannelBeta ||
+         channel == UpdateEngineClient::kReleaseChannelStable;
 }
 
 }  // namespace