Converts most of WorkspaceLayoutManager tests to use common code

ash/common/wm/fullscreen_window_finder.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/common/wm/fullscreen_window_finder.h"
 
 #include "ash/common/shell_window_ids.h"
 #include "ash/common/wm/switchable_windows.h"
 #include "ash/common/wm/window_state.h"
 #include "ash/common/wm_shell.h"
@@ skipping 17 matching lines @@
     topmost_window = active_window;
   } else {
     // Otherwise, use the topmost window on the root window's default container
     // when there is no active window on this root window.
     std::vector<WmWindow*> windows =
         context->GetRootWindow()
             ->GetChildByShellWindowId(kShellWindowId_DefaultContainer)
             ->GetChildren();
     for (auto iter = windows.rbegin(); iter != windows.rend(); ++iter) {
       if ((*iter)->GetWindowState()->IsUserPositionable() &&
-          (*iter)->GetLayer()->GetTargetVisibility()) {
+          (*iter)->GetLayerTargetVisibility()) {
         topmost_window = *iter;
         break;
       }
     }
   }
   while (topmost_window) {
     if (topmost_window->GetWindowState()->IsFullscreen())
       return topmost_window;
     topmost_window = topmost_window->GetTransientParent();
   }
   return nullptr;
 }
 
 }  // namespace wm
 }  // namespace ash