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 4a3628f9eb69855d1cca7afb6afdce58d1fa934e..7a3b890cfa587cfcf799aa9797091a58849f2acc 100644
--- a/components/mus/ws/test_utils.cc
+++ b/components/mus/ws/test_utils.cc
@@ -124,6 +124,15 @@ 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;