Enable overview mode by default.

ash/wm/overview/window_selector_controller.cc

 // Copyright 2013 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/wm/overview/window_selector_controller.h"
 
 #include "ash/session_state_delegate.h"
 #include "ash/shell.h"
 #include "ash/wm/mru_window_tracker.h"
 #include "ash/wm/overview/window_selector.h"
@@ skipping 32 matching lines @@
 }
 
 void WindowSelectorController::HandleCycleWindow(
     WindowSelector::Direction direction) {
   if (!CanSelect())
     return;
 
   if (!IsSelecting()) {
     std::vector<aura::Window*> windows = ash::Shell::GetInstance()->
         mru_window_tracker()->BuildMruWindowList();
+    // Don't cycle with no windows.
+    if (windows.empty())
+      return;
+
     // Removing focus will hide popup windows like the omnibar or open menus.
     window_selector_.reset(
         new WindowSelector(windows, WindowSelector::CYCLE, this));
     window_selector_->Step(direction);
   } else if (window_selector_->mode() == WindowSelector::CYCLE) {
     window_selector_->Step(direction);
   }
 }
 
 bool WindowSelectorController::IsSelecting() {
   return window_selector_.get() != NULL;
 }
 
 void WindowSelectorController::OnWindowSelected(aura::Window* window) {
   window_selector_.reset();
   wm::ActivateWindow(window);
 }
 
 void WindowSelectorController::OnSelectionCanceled() {
   window_selector_.reset();
 }
 
 }  // namespace ash