chromeos: Makes AshTestBase/Helper target mash when appropriate

ash/mus/bridge/wm_shell_mus.cc

Index: ash/mus/bridge/wm_shell_mus.cc
diff --git a/ash/mus/bridge/wm_shell_mus.cc b/ash/mus/bridge/wm_shell_mus.cc
index f63f414f6868f88078f264740d95f6fea1f05357..814fc5f802d9dc937c30270334c650097a1dd120 100644
--- a/ash/mus/bridge/wm_shell_mus.cc
+++ b/ash/mus/bridge/wm_shell_mus.cc
@@ -117,12 +117,14 @@ WmShellMus::WmShellMus(
     WmWindow* primary_root_window,
     std::unique_ptr<ShellDelegate> shell_delegate,
     WindowManager* window_manager,
-    views::PointerWatcherEventRouter* pointer_watcher_event_router)
+    views::PointerWatcherEventRouter* pointer_watcher_event_router,
+    bool create_session_state_delegate_stub)
     : WmShell(std::move(shell_delegate)),
       window_manager_(window_manager),
       primary_root_window_(primary_root_window),
-      pointer_watcher_event_router_(pointer_watcher_event_router),
-      session_state_delegate_(new SessionStateDelegateStub) {
+      pointer_watcher_event_router_(pointer_watcher_event_router) {
+  if (create_session_state_delegate_stub)
+    session_state_delegate_ = base::MakeUnique<SessionStateDelegateStub>();

[James Cook, 2017/02/18 02:23:20]

Should this be session_state_delegate_for_testing_? It seems like the
distinction is test vs. production (which uses Shell).

Also, it might be clearer if WmShellMus just took a unique_ptr<>
session_state_delegate_for_test parameter.

[sky, 2017/02/18 18:00:57]

We were always creating SessionStateDelegateStub before. Maybe you're suggesting
I invert the meaning?
I'm hoping this code is temporary, (the creation of the stub). You and Mike are
more familiar with this. I'm going to redirect this to Mike, who can suggest the
right approach.

   DCHECK(primary_root_window_);
   WmShell::Set(this);
 
@@ -370,7 +372,9 @@ void WmShellMus::OnOverviewModeEnded() {
 }
 
 SessionStateDelegate* WmShellMus::GetSessionStateDelegate() {
-  return session_state_delegate_.get();
+  return session_state_delegate_
+             ? session_state_delegate_.get()
+             : Shell::GetInstance()->session_state_delegate();
 }
 
 void WmShellMus::AddDisplayObserver(WmDisplayObserver* observer) {