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

mojo/shell/public/cpp/lib/application_delegate.cc

Index: mojo/shell/public/cpp/lib/application_delegate.cc
diff --git a/mojo/shell/public/cpp/lib/application_delegate.cc b/mojo/shell/public/cpp/lib/application_delegate.cc
index 5519b840178818c93c8a62ee642b8dfee3fe2edf..7c8426403633fbba47ae4d725740ef7d71f949ed 100644
--- a/mojo/shell/public/cpp/lib/application_delegate.cc
+++ b/mojo/shell/public/cpp/lib/application_delegate.cc
@@ -11,7 +11,8 @@ ApplicationDelegate::ApplicationDelegate() {
 ApplicationDelegate::~ApplicationDelegate() {
 }
 
-void ApplicationDelegate::Initialize(ApplicationImpl* app) {
+void ApplicationDelegate::Initialize(Shell* app, const std::string& url,
+                                     uint32_t id) {
 }
 
 bool ApplicationDelegate::AcceptConnection(ApplicationConnection* connection) {