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 62397ae473372d422fef2f019db6c78ac82e8e54..c78e9a074ed3606d41f90e2dc5611741288754b4 100644
--- a/mash/webtest/webtest.cc
+++ b/mash/webtest/webtest.cc
@@ -155,7 +155,8 @@ 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) {