Make ui::test::EventGenerator work with PointerEvents in mash

ui/aura/test/env_test_helper.h

Index: ui/aura/test/env_test_helper.h
diff --git a/ui/aura/test/env_test_helper.h b/ui/aura/test/env_test_helper.h
index 321615875800796eebb8f422d6cab3c8d0345efa..09d9305a2e3ef0c1d5551239c2a562f0ebb8e4d7 100644
--- a/ui/aura/test/env_test_helper.h
+++ b/ui/aura/test/env_test_helper.h
@@ -32,6 +32,8 @@ class EnvTestHelper {
 
   void SetMode(Env::Mode mode) { env_->mode_ = mode; }
 
+  WindowTreeClient* GetWindowTreeClient() { return env_->window_tree_client_; }
+
   // This circumvents the DCHECKs in Env::SetWindowTreeClient() and should
   // only be used for tests where Env is long lived.
   void SetWindowTreeClient(WindowTreeClient* window_tree_client) {