Use ShellPtr type in ApplicationLoader instead of untyped handles

mojo/public/cpp/application/application_impl.h

Index: mojo/public/cpp/application/application_impl.h
diff --git a/mojo/public/cpp/application/application_impl.h b/mojo/public/cpp/application/application_impl.h
index 430a1246aca48fd75a22c73fa9902021d070f701..5bb9ae87f88715a7d7aec0e0e1190ceab2e7c49a 100644
--- a/mojo/public/cpp/application/application_impl.h
+++ b/mojo/public/cpp/application/application_impl.h
@@ -52,6 +52,10 @@ class ApplicationDelegate;
 //
 class ApplicationImpl : public InterfaceImpl<Application> {
  public:
+  ApplicationImpl(ApplicationDelegate* delegate, ShellPtr shell);
+
+  // TODO(jamesr): Remove these two constructors, the only thing it makes sense
+  // to construct an ApplicationImpl with is a ShellPtr.
   ApplicationImpl(ApplicationDelegate* delegate,
                   ScopedMessagePipeHandle shell_handle);
   ApplicationImpl(ApplicationDelegate* delegate, MojoHandle shell_handle);