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

components/html_viewer/html_document_application_delegate.h

Index: components/html_viewer/html_document_application_delegate.h
diff --git a/components/html_viewer/html_document_application_delegate.h b/components/html_viewer/html_document_application_delegate.h
index 21c6289fb57dda965e5012a5adfee30a94dc2c89..b28dde5e4b3e5a2ed99ab147cc0093b1d0f78ff0 100644
--- a/components/html_viewer/html_document_application_delegate.h
+++ b/components/html_viewer/html_document_application_delegate.h
@@ -15,6 +15,7 @@
 #include "mojo/services/network/public/interfaces/url_loader_factory.mojom.h"
 #include "mojo/shell/public/cpp/application_delegate.h"
 #include "mojo/shell/public/cpp/application_impl.h"
+#include "mojo/shell/public/cpp/shell.h"
 
 namespace html_viewer {
 
@@ -47,7 +48,8 @@ class HTMLDocumentApplicationDelegate : public mojo::ApplicationDelegate,
   void OnTerminate();
 
   // ApplicationDelegate:
-  void Initialize(mojo::ApplicationImpl* app) override;
+  void Initialize(mojo::Shell* shell, const std::string& url,
+                  uint32_t id) override;
   bool AcceptConnection(
       mojo::ApplicationConnection* connection) override;