Add support for uninstalling components and use it in SupervisedUserWhitelistInstaller.

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 28b69c03f6f695d5b5cf0061a66237e101f2c61a..35b3cca3429ba2d94edd2dd9281356a9c79ad1c4 100644
--- a/components/update_client/update_client.h
+++ b/components/update_client/update_client.h
@@ -45,6 +45,11 @@ class ComponentInstaller
   virtual bool GetInstalledFile(const std::string& file,
                                 base::FilePath* installed_file) = 0;
 
+  // Called by the component updater when a component has been unregistered and
+  // all versions should be uninstalled from disk. Returns true if
+  // uninstallation is supported, false otherwise.
+  virtual bool Uninstall() = 0;
+
  protected:
   friend class base::RefCountedThreadSafe<ComponentInstaller>;