ui: Cleanup class/struct forward declarations

chrome/browser/component_updater/sth_set_component_installer.h

Index: chrome/browser/component_updater/sth_set_component_installer.h
diff --git a/chrome/browser/component_updater/sth_set_component_installer.h b/chrome/browser/component_updater/sth_set_component_installer.h
index 1523d7a011814ce8f00b6c85fbe824c8b9022c1c..0afadb48bb7fc8655c9611e4a6c87d8921fdbb14 100644
--- a/chrome/browser/component_updater/sth_set_component_installer.h
+++ b/chrome/browser/component_updater/sth_set_component_installer.h
@@ -50,8 +50,9 @@ class STHSetComponentInstallerTraits : public ComponentInstallerTraits {
   // ComponentInstallerTraits implementation.
   bool SupportsGroupPolicyEnabledComponentUpdates() const override;
   bool RequiresNetworkEncryption() const override;
-  bool OnCustomInstall(const base::DictionaryValue& manifest,
-                       const base::FilePath& install_dir) override;
+  update_client::CrxInstaller::Result OnCustomInstall(
+      const base::DictionaryValue& manifest,
+      const base::FilePath& install_dir) override;
   bool VerifyInstallation(const base::DictionaryValue& manifest,
                           const base::FilePath& install_dir) const override;
   void ComponentReady(const base::Version& version,