wm: Allow double tap on overview button to quick switch.

ash/system/overview/overview_button_tray.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/system/overview/overview_button_tray.h"
 
 #include "ash/resources/vector_icons/vector_icons.h"
 #include "ash/session/session_controller.h"
 #include "ash/shelf/shelf_constants.h"
 #include "ash/shell.h"
 #include "ash/shell_port.h"
 #include "ash/strings/grit/ash_strings.h"
 #include "ash/system/tray/tray_constants.h"
 #include "ash/system/tray/tray_container.h"
 #include "ash/wm/maximize_mode/maximize_mode_controller.h"
+#include "ash/wm/mru_window_tracker.h"
 #include "ash/wm/overview/window_selector_controller.h"
+#include "ash/wm_window.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/gfx/paint_vector_icon.h"
 #include "ui/views/border.h"
 #include "ui/views/controls/image_view.h"
+#include "ui/wm/core/window_util.h"
 
 namespace ash {
 
 OverviewButtonTray::OverviewButtonTray(WmShelf* wm_shelf)
     : TrayBackgroundView(wm_shelf),
       icon_(new views::ImageView()),
       scoped_session_observer_(this) {
   SetInkDropMode(InkDropMode::ON);
 
   gfx::ImageSkia image =
@@ skipping 14 matching lines @@
 
 OverviewButtonTray::~OverviewButtonTray() {
   Shell::Get()->RemoveShellObserver(this);
 }
 
 void OverviewButtonTray::UpdateAfterLoginStatusChange(LoginStatus status) {
   UpdateIconVisibility();
 }
 
 bool OverviewButtonTray::PerformAction(const ui::Event& event) {
+  if (event.type() == ui::ET_GESTURE_TAP) {
+    if (event.AsGestureEvent()->details().tap_count() == 2) {
+      // Ignore double taps if we are on the window selection page.
+      if (Shell::Get()->window_selector_controller()->IsSelecting())
+        return true;
+
+      MruWindowTracker::WindowList mru_window_list =
+          Shell::Get()->mru_window_tracker()->BuildMruWindowList();
+
+      // Switch to the second most recently used window (most recent is the
+      // current window), if it exists.
+      if (mru_window_list.size() > 1) {
+        AnimateInkDrop(views::InkDropState::DEACTIVATED, nullptr);
+        ::wm::ActivateWindow(WmWindow::GetAuraWindow(mru_window_list[1]));
+        return true;
+      }
+    }
+  }
+
   WindowSelectorController* controller =
       Shell::Get()->window_selector_controller();
-  // Toggling overview mode will fail if there is no window to show.
+  // Note: Toggling overview mode will fail if there is no window to show, the
+  // screen is locked, a modal dialog is open or is running in kiosk app
+  // session.
   bool performed = controller->ToggleOverview();
   ShellPort::Get()->RecordUserMetricsAction(UMA_TRAY_OVERVIEW);
   return performed;
 }
 
 void OverviewButtonTray::OnSessionStateChanged(
     session_manager::SessionState state) {
   UpdateIconVisibility();
 }
 
@@ skipping 35 matching lines @@
   SetVisible(
       shell->maximize_mode_controller()->IsMaximizeModeWindowManagerEnabled() &&
       session_controller->IsActiveUserSessionStarted() &&
       !session_controller->IsScreenLocked() &&
       session_controller->GetSessionState() ==
           session_manager::SessionState::ACTIVE &&
       !session_controller->IsKioskSession());
 }
 
 }  // namespace ash