ash: Add RootWindowHostFactory class.

ash/shell/shell_delegate_impl.cc

Index: ash/shell/shell_delegate_impl.cc
diff --git a/ash/shell/shell_delegate_impl.cc b/ash/shell/shell_delegate_impl.cc
index 8cf97ba227123501ad69f60040e30a2615074b83..a75893f266801f368dfba5b4dbab180cc892e57c 100644
--- a/ash/shell/shell_delegate_impl.cc
+++ b/ash/shell/shell_delegate_impl.cc
@@ -5,6 +5,7 @@
 #include "ash/shell/shell_delegate_impl.h"
 
 #include "ash/caps_lock_delegate_stub.h"
+#include "ash/host/root_window_host_factory.h"
 #include "ash/shell/example_factory.h"
 #include "ash/shell/launcher_delegate_impl.h"
 #include "ash/shell/context_menu.h"
@@ -212,5 +213,9 @@ bool ShellDelegateImpl::IsSearchKeyActingAsFunctionKey() const {
   return false;
 }
 
+RootWindowHostFactory* ShellDelegateImpl::CreateRootWindowHostFactory() {
+  return RootWindowHostFactory::Create();
+}
+
 }  // namespace shell
 }  // namespace ash