Two fixes for mash browser_tests on chromes

ash/mus/root_window_controller.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/mus/root_window_controller.h"
 
 #include <stdint.h>
 
 #include <map>
 #include <sstream>
@@ skipping 179 matching lines @@
     // TODO(sky): likely want to constrain more than root size.
     const gfx::Size max_size = root_->bounds().size();
     width = std::max(0, std::min(max_size.width(), pref.width()));
     height = std::max(0, std::min(max_size.height(), pref.height()));
   }
   return gfx::Rect(40 + (window_count_ % 4) * 40, 40 + (window_count_ % 4) * 40,
                    width, height);
 }
 
 void RootWindowController::OnShelfWindowAvailable() {
-  DockedWindowLayoutManager::Get(WmWindowMus::Get(root_))
-      ->SetShelf(wm_shelf_.get());
+  DockedWindowLayoutManager* docked_window_layout_manager =
+      DockedWindowLayoutManager::Get(WmWindowMus::Get(root_));
+
+  // Following code expects the shelf to be called only once.
+  // TODO(sky): this check is only necessary while we have shelf hosted in
+  // sysui (as sysui can restart). Once that is fixed there should be a DCHECK
+  // that the shelf hasn't been set.
+  if (docked_window_layout_manager->shelf())
+    return;
+
+  docked_window_layout_manager->SetShelf(wm_shelf_.get());
 
   PanelLayoutManager::Get(WmWindowMus::Get(root_))->SetShelf(wm_shelf_.get());
 
   // TODO: http://crbug.com/614182 Ash's ShelfLayoutManager implements
   // DockedWindowLayoutManagerObserver so that it can inset by the docked
   // windows.
   // docked_layout_manager_->AddObserver(shelf_->shelf_layout_manager());
 }
 
 void RootWindowController::CreateLayoutManagers() {
@@ skipping 34 matching lines @@
       base::WrapUnique(new DockedWindowLayoutManager(docked_container)));
 
   WmWindowMus* panel_container =
       GetWindowByShellWindowId(kShellWindowId_PanelContainer);
   panel_container->SetLayoutManager(
       base::WrapUnique(new PanelLayoutManager(panel_container)));
 }
 
 }  // namespace mus
 }  // namespace ash