Converts mash_wm_apptests to unit tests

mash/wm/window_manager_unittest.cc

Index: mash/wm/window_manager_unittest.cc
diff --git a/mash/wm/window_manager_apptest.cc b/mash/wm/window_manager_unittest.cc
similarity index 87%
rename from mash/wm/window_manager_apptest.cc
rename to mash/wm/window_manager_unittest.cc
index 605b8255ccd7ca7888991b1fb62f5e4669d1be86..5b9e16deaededed5f4c6e6f27d973967f41d4729 100644
--- a/mash/wm/window_manager_apptest.cc
+++ b/mash/wm/window_manager_unittest.cc
@@ -11,7 +11,7 @@
 #include "components/mus/public/cpp/window_tree_connection.h"
 #include "components/mus/public/cpp/window_tree_delegate.h"
 #include "components/mus/public/interfaces/window_tree.mojom.h"
-#include "mojo/shell/public/cpp/application_test_base.h"
+#include "mojo/shell/public/cpp/shell_test.h"
 
 namespace mash {
 namespace wm {
@@ -29,13 +29,20 @@ class WindowTreeDelegateImpl : public mus::WindowTreeDelegate {
   DISALLOW_COPY_AND_ASSIGN(WindowTreeDelegateImpl);
 };
 
-using WindowManagerAppTest = mojo::test::ApplicationTestBase;
+class WindowManagerTest : public mojo::test::ShellTest {
+ public:
+  WindowManagerTest() : mojo::test::ShellTest("exe:mash_unittests") {}
+  ~WindowManagerTest() override {}
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(WindowManagerTest);
+};
 
 void OnEmbed(bool success) {
   ASSERT_TRUE(success);
 }
 
-TEST_F(WindowManagerAppTest, OpenWindow) {
+TEST_F(WindowManagerTest, OpenWindow) {
   WindowTreeDelegateImpl window_tree_delegate;
 
   // Bring up the the desktop_wm.