mash: make Env::last_mouse_location() accurate for Mus

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 2402f3cff0f2ac2dc484f4baec78899dae86c461..321615875800796eebb8f422d6cab3c8d0345efa 100644
--- a/ui/aura/test/env_test_helper.h
+++ b/ui/aura/test/env_test_helper.h
@@ -38,6 +38,10 @@ class EnvTestHelper {
     env_->window_tree_client_ = window_tree_client;
   }
 
+  void SetAlwaysUseLastMouseLocation(bool value) {
+    env_->always_use_last_mouse_location_ = value;
+  }
+
  private:
   Env* env_;