Add window overview mode behind --ash-enable-overview-mode flag to F5 key.

ash/wm/window_cycle_controller.cc

Index: ash/wm/window_cycle_controller.cc
diff --git a/ash/wm/window_cycle_controller.cc b/ash/wm/window_cycle_controller.cc
index 89af6c1836f8548ee56c5c4ded9f0eed40dabd9c..798123afe730ce0770e6e7dca52fe9b8e15c0499 100644
--- a/ash/wm/window_cycle_controller.cc
+++ b/ash/wm/window_cycle_controller.cc
@@ -11,6 +11,7 @@
 #include "ash/shell_window_ids.h"
 #include "ash/wm/activation_controller.h"
 #include "ash/wm/window_cycle_list.h"
+#include "ash/wm/window_selector.h"
 #include "ash/wm/window_util.h"
 #include "ash/wm/workspace_controller.h"
 #include "ui/aura/root_window.h"
@@ -164,6 +165,31 @@ void WindowCycleController::AltKeyReleased() {
   StopCycling();
 }
 
+void WindowCycleController::ToggleOverview() {
+  if (window_selector_.get()) {
+    window_selector_.reset();
+  } else {
+    std::vector<aura::Window*> windows = BuildWindowList(NULL, false);
+    // Don't enter overview mode with no windows.
+    if (windows.empty())
+      return;
+
+    // Deactivating the window will hide popup windows like the omnibar or
+    // open menus.
+    aura::Window* active_window = wm::GetActiveWindow();
+    if (active_window)
+      wm::DeactivateWindow(active_window);
+    window_selector_.reset(new WindowSelector(windows, this));
+  }
+}
+
+void WindowCycleController::SelectWindow(aura::Window* window) {
+  window_selector_.reset();
+  wm::ActivateWindow(window);
+  mru_windows_.remove(window);
+  mru_windows_.push_front(window);
+}
+
 // static
 std::vector<aura::Window*> WindowCycleController::BuildWindowList(
     const std::list<aura::Window*>* mru_windows,