Add support for uninstalling components and use it in SupervisedUserWhitelistInstaller.

components/update_client/crx_update_item.h

Index: components/update_client/crx_update_item.h
diff --git a/components/update_client/crx_update_item.h b/components/update_client/crx_update_item.h
index ba38a1b6c8694e9292998d2255f6c8ff90acba1a..09af62fde432687171cfe092d9196281f90f8210 100644
--- a/components/update_client/crx_update_item.h
+++ b/components/update_client/crx_update_item.h
@@ -71,6 +71,10 @@ struct CrxUpdateItem {
   // enforce conditions or notify observers of the change.
   Status status;
 
+  // True if the component was recently unregistered and will be uninstalled
+  // soon (after the currently operation is finished, if there is one).
+  bool unregistered;
+
   std::string id;
   CrxComponent component;