Adds remainder of support for multiple roots to WS

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

Index: components/mus/public/cpp/tests/test_window_tree.cc
diff --git a/components/mus/public/cpp/tests/test_window_tree.cc b/components/mus/public/cpp/tests/test_window_tree.cc
index c401a8e5bfb2f8527f962d6020da90127eae4fbd..0ecd6f249be938a965cb633ebedc49b788aadde1 100644
--- a/components/mus/public/cpp/tests/test_window_tree.cc
+++ b/components/mus/public/cpp/tests/test_window_tree.cc
@@ -8,7 +8,8 @@
 
 namespace mus {
 
-TestWindowTree::TestWindowTree() : got_change_(false), change_id_(0) {}
+TestWindowTree::TestWindowTree()
+    : got_change_(false), change_id_(0), window_id_(0u) {}
 
 TestWindowTree::~TestWindowTree() {}
 
@@ -31,6 +32,15 @@ void TestWindowTree::NewWindow(
     uint32_t window_id,
     mojo::Map<mojo::String, mojo::Array<uint8_t>> properties) {}
 
+void TestWindowTree::NewTopLevelWindow(
+    uint32_t change_id,
+    uint32_t window_id,
+    mojo::Map<mojo::String, mojo::Array<uint8_t>> properties) {
+  got_change_ = true;
+  change_id_ = change_id;
+  window_id_ = window_id;
+}
+
 void TestWindowTree::DeleteWindow(uint32_t change_id, uint32_t window_id) {}
 
 void TestWindowTree::SetWindowBounds(uint32_t change_id,