Separated alt-tab window cycle from overview mode

ash/wm/window_cycle_list.h

Index: ash/wm/window_cycle_list.h
diff --git a/ash/wm/window_cycle_list.h b/ash/wm/window_cycle_list.h
new file mode 100644
index 0000000000000000000000000000000000000000..d8b12776979e575135a6309975cf03a1b634a9aa
--- /dev/null
+++ b/ash/wm/window_cycle_list.h
@@ -0,0 +1,64 @@
+// Copyright (c) 2012 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.
+
+#ifndef ASH_WM_WINDOW_CYCLE_LIST_H_
+#define ASH_WM_WINDOW_CYCLE_LIST_H_
+
+#include <vector>
+
+#include "ash/ash_export.h"
+#include "base/basictypes.h"
+#include "base/compiler_specific.h"
+#include "base/memory/scoped_ptr.h"
+#include "ui/aura/window_observer.h"
+
+namespace ash {
+class ScopedShowWindow;
+
+// Tracks a set of Windows that can be stepped through. This class is used by
+// the WindowCycleController.
+class ASH_EXPORT WindowCycleList : public aura::WindowObserver {
+ public:
+  typedef std::vector<aura::Window*> WindowList;
+
+  enum Direction {
+    FORWARD,
+    BACKWARD
+  };
+
+  explicit WindowCycleList(const WindowList& windows);
+  virtual ~WindowCycleList();
+
+  bool empty() const { return windows_.empty(); }
+
+  // Cycles to the next or previous window based on |direction|.
+  void Step(Direction direction);
+
+  const WindowList& windows() const { return windows_; }
+
+ private:
+  // Returns the index of |window| in |windows_| or -1 if it isn't there.
+  int GetWindowIndex(aura::Window* window);
+
+  // aura::WindowObserver overrides:
+  virtual void OnWindowDestroyed(aura::Window* window) OVERRIDE;

[tdanderson, 2014/05/01 18:51:39]

IIUC, a WindowCycleList only exists while Alt+Tab cycling is in progress. How
can windows get destroyed during cycling? (i.e., why is it necessary to have
WindowCycleList be a WindowObserver?)

If it is possible for windows to be destroyed during a cycle session, you should
definitely explain that (perhaps in your comment block at line 47)

[Nina, 2014/05/01 20:41:16]

Some factors like JS close method can trigger a window destruction without
interaction from the user. If we don't take that into account, we could try to
dereference a dead pointer. Should I write that in a comment, then? I don't
think there's a design to allow the user to close windows from alt-tab mode.

[tdanderson, 2014/05/01 21:58:33]

OK, sounds good. Does a similar possibility exist for new windows being opened
during cycling?
Yes, I would add a brief comment to explain why it's there, since someone may
otherwise get the impression that the user is somehow able to close windows
during cycling.

[Nina, 2014/05/02 13:27:33]

Done. I don't know if it's possible to observe the creation of new windows.
Anyway that is not too important - if a window is created while window cycling,
you won't be able to get to it until you release alt and start cycling again but
chrome won't explode.

+
+  // List of weak pointers to windows to use while cycling with the keyboard.
+  // List is built when the user initiates the gesture (e.g. hits alt-tab the
+  // first time) and is emptied when the gesture is complete (e.g. releases the
+  // alt key).
+  WindowList windows_;
+
+  // Current position in the |windows_| list or -1 if we're not cycling.

[tdanderson, 2014/05/01 18:51:39]

Similar comment to the one above: if this object exists, doesn't that mean we're
currently cycling? I don't think this should ever be allowed to have a -1 value.
See my comment in window_cycle_list.cc, line 144.

[Nina, 2014/05/02 13:27:33]

Done.

+  int current_index_;
+
+  // Wrapper for the window brought to the front.
+  scoped_ptr<ScopedShowWindow> showing_window_;
+
+  DISALLOW_COPY_AND_ASSIGN(WindowCycleList);
+};
+
+}  // namespace ash
+
+#endif  // ASH_WM_WINDOW_CYCLE_LIST_H_