Add support for uninstalling components and use it in SupervisedUserWhitelistInstaller.

components/component_updater/component_updater_service.h

Index: components/component_updater/component_updater_service.h
diff --git a/components/component_updater/component_updater_service.h b/components/component_updater/component_updater_service.h
index 56706191badb6679b532c870873be58c206443b8..ac60a7f8e87b2dc5833a272adf6998ed8c0de722 100644
--- a/components/component_updater/component_updater_service.h
+++ b/components/component_updater/component_updater_service.h
@@ -124,6 +124,14 @@ class ComponentUpdateService {
   virtual Status RegisterComponent(
       const update_client::CrxComponent& component) = 0;
 
+  // Unregisters the component with the given ID. This means that the component
+  // is not going to be included in future update checks. If a download or
+  // update operation for the component is currently in progress, it will
+  // silently finish without triggering the next step.
+  // Note that the installer for the component is responsible for removing any
+  // existing versions of the component from disk.
+  virtual Status UnregisterComponent(const std::string& crx_id) = 0;
+
   // Returns a list of registered components.
   virtual std::vector<std::string> GetComponentIDs() const = 0;