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

ash/mus/window_manager.h

Index: ash/mus/window_manager.h
diff --git a/ash/mus/window_manager.h b/ash/mus/window_manager.h
index 73d675a12c8081349e9a5e3b603101c7bbec1706..4daca5bf2069c4f6a463d12e5e8d4dca656d2660 100644
--- a/ash/mus/window_manager.h
+++ b/ash/mus/window_manager.h
@@ -46,6 +46,7 @@ class ScreenMus;
 class ShellDelegate;
 
 namespace test {
+class AshEventGeneratorDelegate;
 class AshTestHelper;
 }
 
@@ -105,7 +106,8 @@ class WindowManager : public aura::WindowManagerDelegate,
       std::unique_ptr<aura::WindowTreeHostMus> window_tree_host);
 
  private:
-  friend class ash::test::AshTestHelper;
+  friend class test::AshEventGeneratorDelegate;
+  friend class test::AshTestHelper;
   friend class WmTestHelper;
 
   using RootWindowControllers = std::set<std::unique_ptr<RootWindowController>>;