mus: Add views_mus_interactive_ui_tests target

ui/views/mus/platform_test_helper_mus.cc

Index: ui/views/mus/platform_test_helper_mus.cc
diff --git a/ui/views/mus/platform_test_helper_mus.cc b/ui/views/mus/platform_test_helper_mus.cc
index bffdbc6a6eff1b122d06b100f8102a6123e1ab92..06fe84e91d07c5eae9050c0a6eeed99ac484cfa3 100644
--- a/ui/views/mus/platform_test_helper_mus.cc
+++ b/ui/views/mus/platform_test_helper_mus.cc
@@ -66,8 +66,6 @@ class PlatformTestHelperMus : public PlatformTestHelper {
     shell_connection_.reset();
   }
 
-  bool IsMus() const override { return true; }
-
  private:
   NativeWidget* CreateNativeWidgetMus(
       const std::map<std::string, std::vector<uint8_t>>& props,
@@ -96,4 +94,9 @@ std::unique_ptr<PlatformTestHelper> PlatformTestHelper::Create() {
   return base::WrapUnique(new PlatformTestHelperMus);
 }
 
+// static
+bool PlatformTestHelper::IsMus() {
+  return true;
+}
+
 }  // namespace views