Don't handle the tab press event in the window cycle event filter.

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 24d05f1a93cfba89ff079c5460d973f5a5549177..f1250d9081e4843a2286dd4a58ff0def9c829ed9 100644
--- a/ash/wm/window_cycle_controller.cc
+++ b/ash/wm/window_cycle_controller.cc
@@ -46,9 +46,13 @@ WindowCycleEventFilter::~WindowCycleEventFilter() {
 }
 
 void WindowCycleEventFilter::OnKeyEvent(ui::KeyEvent* event) {
-  // Until the alt key is released, all key events are handled by this window
-  // cycle controller: https://crbug.com/340339.
-  event->StopPropagation();
+  // Until the alt key is released, all key events except the tab press (which
+  // is handled by the accelerator controller to call Step) are handled by this
+  // window cycle controller: https://crbug.com/340339.
+  if (event->key_code() != ui::VKEY_TAB ||
+      event->type() != ui::ET_KEY_PRESSED) {
+    event->StopPropagation();
+  }
   // Views uses VKEY_MENU for both left and right Alt keys.
   if (event->key_code() == ui::VKEY_MENU &&
       event->type() == ui::ET_KEY_RELEASED) {