views/mus: Have explicit ownership of views::WindowManagerConnection.

mash/webtest/webtest.cc

Index: mash/webtest/webtest.cc
diff --git a/mash/webtest/webtest.cc b/mash/webtest/webtest.cc
index e391e679110fb23976ae518ad818b6ca58b1aec6..9f5f65c509343a8bf276005d172a8c8c67f6a43f 100644
--- a/mash/webtest/webtest.cc
+++ b/mash/webtest/webtest.cc
@@ -154,7 +154,8 @@ void Webtest::Initialize(shell::Connector* connector,
   tracing_.Initialize(connector, identity.name());
 
   aura_init_.reset(new views::AuraInit(connector, "views_mus_resources.pak"));
-  views::WindowManagerConnection::Create(connector, identity);
+  window_manager_connection_ =
+      views::WindowManagerConnection::Create(connector, identity);
 }
 
 bool Webtest::AcceptConnection(shell::Connection* connection) {