Reland: mus: Enable system modal windows

components/mus/ws/test_utils.cc

Index: components/mus/ws/test_utils.cc
diff --git a/components/mus/ws/test_utils.cc b/components/mus/ws/test_utils.cc
index 43953f0d0d868a465f26929531b218a36c871e26..808d86f2df9ff3f9bf17f1d1e57757316e36f90f 100644
--- a/components/mus/ws/test_utils.cc
+++ b/components/mus/ws/test_utils.cc
@@ -122,6 +122,15 @@ DisplayTestApi::~DisplayTestApi() {}
 
 // EventDispatcherTestApi  ----------------------------------------------------
 
+bool EventDispatcherTestApi::IsWindowPointerTarget(
+    const ServerWindow* window) const {
+  for (const auto& pair : ed_->pointer_targets_) {
+    if (pair.second.window == window)
+      return true;
+  }
+  return false;
+}
+
 int EventDispatcherTestApi::NumberPointerTargetsForWindow(
     ServerWindow* window) {
   int count = 0;