Refactor the UpdateEngine and its actions in the component updater.

components/update_client/update_client.h

Index: components/update_client/update_client.h
diff --git a/components/update_client/update_client.h b/components/update_client/update_client.h
index 412a4d9b264488cb3959b22bfaebbc009cbeed60..d068a5654bf29104df086c5f9c4f5ae9b98f3fc1 100644
--- a/components/update_client/update_client.h
+++ b/components/update_client/update_client.h
@@ -143,6 +143,22 @@ class Configurator;
 enum class Error;
 struct CrxUpdateItem;
 
+enum class ComponentState {
+  kNew,
+  kChecking,
+  kCanUpdate,
+  kDownloadingDiff,
+  kDownloading,
+  kDownloaded,
+  kUpdatingDiff,
+  kUpdating,
+  kUpdated,
+  kUpToDate,
+  kUpdateError,
+  kUninstalled,
+  kLastStatus
+};
+
 // Called when a non-blocking call in this module completes.
 using Callback = base::Callback<void(Error error)>;
 
@@ -252,7 +268,7 @@ class UpdateClient : public base::RefCounted<UpdateClient> {
    public:
     enum class Events {
       // Sent before the update client does an update check.
-      COMPONENT_CHECKING_FOR_UPDATES,
+      COMPONENT_CHECKING_FOR_UPDATES = 1,
 
       // Sent when there is a new version of a registered CRX. After
       // the notification is sent the CRX will be downloaded unless the