Extract shell methods from ApplicationImpl into a base class, and pass this to Initialize() instead.

mojo/shell/shell_application_delegate.cc

Index: mojo/shell/shell_application_delegate.cc
diff --git a/mojo/shell/shell_application_delegate.cc b/mojo/shell/shell_application_delegate.cc
index 66a36bafbf183444eebe928cc405c7cc56d54280..e472617e6a80bd285691154399ab0c129a0f71e6 100644
--- a/mojo/shell/shell_application_delegate.cc
+++ b/mojo/shell/shell_application_delegate.cc
@@ -21,7 +21,8 @@ ShellApplicationDelegate::ShellApplicationDelegate(
     : manager_(manager) {}
 ShellApplicationDelegate::~ShellApplicationDelegate() {}
 
-void ShellApplicationDelegate::Initialize(ApplicationImpl* app) {}
+void ShellApplicationDelegate::Initialize(Shell* shell, const std::string& url,
+                                          uint32_t id) {}
 bool ShellApplicationDelegate::AcceptConnection(
     ApplicationConnection* connection) {
   connection->AddService<mojom::ApplicationManager>(this);