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

mojo/public/cpp/bindings/tests/versioning_apptest.cc

Index: mojo/public/cpp/bindings/tests/versioning_apptest.cc
diff --git a/mojo/public/cpp/bindings/tests/versioning_apptest.cc b/mojo/public/cpp/bindings/tests/versioning_apptest.cc
index 26dca60a73c5fe705938caaeb5e8fb297e1da484..450557ad8d840a3038f234c9d3fd06903816e867 100644
--- a/mojo/public/cpp/bindings/tests/versioning_apptest.cc
+++ b/mojo/public/cpp/bindings/tests/versioning_apptest.cc
@@ -7,8 +7,8 @@
 
 #include "mojo/public/cpp/system/macros.h"
 #include "mojo/public/interfaces/bindings/tests/versioning_test_client.mojom.h"
-#include "mojo/shell/public/cpp/application_impl.h"
 #include "mojo/shell/public/cpp/application_test_base.h"
+#include "mojo/shell/public/cpp/shell.h"
 
 namespace mojo {
 namespace test {
@@ -24,8 +24,7 @@ class VersioningApplicationTest : public ApplicationTestBase {
   void SetUp() override {
     ApplicationTestBase::SetUp();
 
-    application_impl()->ConnectToService("mojo:versioning_test_service",
-                                         &database_);
+    shell()->ConnectToService("mojo:versioning_test_service", &database_);
   }
 
   HumanResourceDatabasePtr database_;