Converts MruWindowTracker to work with common types

ash/common/wm/focus_rules.cc

Index: ash/common/wm/focus_rules.cc
diff --git a/ash/common/wm/focus_rules.cc b/ash/common/wm/focus_rules.cc
new file mode 100644
index 0000000000000000000000000000000000000000..3fd02b758c12957e9afa100176e88674ef4b8448
--- /dev/null
+++ b/ash/common/wm/focus_rules.cc
@@ -0,0 +1,55 @@
+// Copyright 2016 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/focus_rules.h"
+
+#include "ash/common/shell_window_ids.h"
+#include "ash/common/wm/window_state.h"
+#include "ash/common/wm_shell.h"
+#include "ash/common/wm_window.h"
+
+namespace ash {
+
+bool IsToplevelWindow(WmWindow* window) {
+  // The window must in a valid hierarchy.
+  if (!window->GetRootWindow())
+    return false;
+
+  // The window must exist within a container that supports activation.
+  // The window cannot be blocked by a modal transient.
+  return IsActivatableShellWindowId(window->GetParent()->GetShellWindowId());
+}
+
+bool IsWindowConsideredActivatable(WmWindow* window) {

[James Cook, 2016/06/07 01:21:04]

Do you need to handle a null window? I see the BaseFocusRules version does,
though the ash version does not.

[sky, 2016/06/07 02:46:21]

Seem weird to me to null check. I added a DCHECK.

+  // Only toplevel windows can be activated.
+  if (!IsToplevelWindow(window))
+    return false;
+
+  // The window must be visible.
+  return IsWindowConsideredVisibleForActivation(window);
+}
+
+bool IsWindowConsideredVisibleForActivation(WmWindow* window) {
+  // If the |window| doesn't belong to the current active user and also doesn't
+  // show for the current active user, then it should not be activated.
+  if (!WmShell::Get()->CanShowWindowForUser(window))
+    return false;
+
+  if (window->IsVisible())
+    return true;
+
+  // Minimized windows are hidden in their minimized state, but they can always
+  // be activated.
+  if (window->GetWindowState()->IsMinimized())
+    return true;
+
+  if (!window->GetTargetVisibility())
+    return false;
+
+  const int parent_shell_window_id = window->GetParent()->GetShellWindowId();
+  return parent_shell_window_id == kShellWindowId_DefaultContainer ||
+         parent_shell_window_id == kShellWindowId_LockScreenContainer;
+}
+
+}  // namespace ash