Convert mus apptests to shelltests

components/mus/public/cpp/tests/window_server_test_base.cc

Index: components/mus/public/cpp/tests/window_server_test_base.cc
diff --git a/components/mus/public/cpp/tests/window_server_test_base.cc b/components/mus/public/cpp/tests/window_server_test_base.cc
index affbf31a4beefa8f43058cc675197a29e33adfbc..445358a8178c8176f6da0115424b2e7fae7c85e2 100644
--- a/components/mus/public/cpp/tests/window_server_test_base.cc
+++ b/components/mus/public/cpp/tests/window_server_test_base.cc
@@ -63,7 +63,7 @@ bool WindowServerTestBase::QuitRunLoop() {
 }
 
 void WindowServerTestBase::SetUp() {
-  ApplicationTestBase::SetUp();
+  WindowManagerShellTestBase::SetUp();
 
   CreateWindowTreeHost(connector(), this, &host_, this);
 
@@ -71,10 +71,6 @@ void WindowServerTestBase::SetUp() {
   std::swap(window_manager_, most_recent_connection_);
 }
 
-mojo::ShellClient* WindowServerTestBase::GetShellClient() {
-  return this;
-}
-
 bool WindowServerTestBase::AcceptConnection(mojo::Connection* connection) {
   connection->AddInterface<mojom::WindowTreeClient>(this);
   return true;