Enable ash window cycle UI by default.

ash/common/wm/window_cycle_controller.cc

 // Copyright 2014 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/window_cycle_controller.h"
 
 #include "ash/common/metrics/task_switch_source.h"
 #include "ash/common/session/session_state_delegate.h"
+#include "ash/common/shell_window_ids.h"
 #include "ash/common/wm/mru_window_tracker.h"
 #include "ash/common/wm/window_cycle_event_filter.h"
 #include "ash/common/wm/window_cycle_list.h"
 #include "ash/common/wm_shell.h"
+#include "ash/common/wm_window.h"
 #include "base/metrics/histogram.h"
 
 namespace ash {
 
 namespace {
 
 // Returns the most recently active window from the |window_list| or nullptr
 // if the list is empty.
 WmWindow* GetActiveWindow(const MruWindowTracker::WindowList& window_list) {
   return window_list.empty() ? nullptr : window_list[0];
@@ skipping 22 matching lines @@
 
   if (!IsCycling())
     StartCycling();
 
   Step(direction);
 }
 
 void WindowCycleController::StartCycling() {
   MruWindowTracker::WindowList window_list =
       WmShell::Get()->mru_window_tracker()->BuildMruWindowList();
+  // Exclude the AppList window, which will hide as soon as cycling starts
+  // anyway. It doesn't make sense to count it as a "switchable" window, yet
+  // a lot of code relies on the MRU list returning the app window. If we
+  // don't manually remove it, the window cycling UI won't crash or misbehave,
+  // but there will be a flicker as the target window changes.
+  window_list.erase(std::remove_if(window_list.begin(), window_list.end(),
+                                   [](WmWindow* window) {
+                                     return window->GetRootWindow()
+                                         ->GetChildByShellWindowId(
+                                             kShellWindowId_AppListContainer)
+                                         ->Contains(window);
+                                   }),
+                    window_list.end());
 
   active_window_before_window_cycle_ = GetActiveWindow(window_list);
 
   window_cycle_list_.reset(new WindowCycleList(window_list));
   event_filter_ = WmShell::Get()->CreateWindowCycleEventFilter();
   cycle_start_time_ = base::Time::Now();
   WmShell::Get()->RecordUserMetricsAction(UMA_WINDOW_CYCLE);
   UMA_HISTOGRAM_COUNTS_100("Ash.WindowCycleController.Items",
                            window_list.size());
 }
@@ skipping 21 matching lines @@
 
   if (active_window_after_window_cycle != nullptr &&
       active_window_before_window_cycle_ != active_window_after_window_cycle) {
     WmShell::Get()->RecordTaskSwitchMetric(
         TaskSwitchSource::WINDOW_CYCLE_CONTROLLER);
   }
   active_window_before_window_cycle_ = nullptr;
 }
 
 }  // namespace ash