Adds remainder of support for multiple roots to WS

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

Index: components/mus/public/cpp/tests/test_window_tree.h
diff --git a/components/mus/public/cpp/tests/test_window_tree.h b/components/mus/public/cpp/tests/test_window_tree.h
index 3ca5c81ffdf2922aa8efdcc2d94859b8bde733cc..3115b27174d7eaa35b0c75a27511e5811a5fe6a6 100644
--- a/components/mus/public/cpp/tests/test_window_tree.h
+++ b/components/mus/public/cpp/tests/test_window_tree.h
@@ -25,6 +25,8 @@ class TestWindowTree : public mojom::WindowTree {
   // invoked since the last GetAndClearChangeId().
   bool GetAndClearChangeId(uint32_t* change_id);
 
+  uint32_t window_id() const { return window_id_; }
+
   bool WasEventAcked(uint32_t event_id) const;
 
  private:
@@ -33,6 +35,10 @@ class TestWindowTree : public mojom::WindowTree {
       uint32_t change_id,
       uint32_t window_id,
       mojo::Map<mojo::String, mojo::Array<uint8_t>> properties) override;
+  void NewTopLevelWindow(
+      uint32_t change_id,
+      uint32_t window_id,
+      mojo::Map<mojo::String, mojo::Array<uint8_t>> properties) override;
   void DeleteWindow(uint32_t change_id, uint32_t window_id) override;
   void SetWindowBounds(uint32_t change_id,
                        uint32_t window_id,
@@ -87,6 +93,7 @@ class TestWindowTree : public mojom::WindowTree {
   bool got_change_;
   uint32_t change_id_;
   std::set<uint32_t> acked_events_;
+  uint32_t window_id_;
 
   DISALLOW_COPY_AND_ASSIGN(TestWindowTree);
 };