ash: Start/stop observing KeyboardController via ShellObserver

ash/common/keyboard/keyboard_observer_register.cc

+// Copyright 2017 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/keyboard/keyboard_observer_register.h"
+
+#include "ui/keyboard/keyboard_controller.h"
+
+namespace ash {
+
+void UpdateKeyboardObserverFromStateChanged(
+    bool keyboard_activated,
+    WmWindow* keyboard_root_window,
+    WmWindow* observer_root_window,
+    ScopedObserver<keyboard::KeyboardController,
+                   keyboard::KeyboardControllerObserver>* keyboard_observer) {
+  if (keyboard_root_window != observer_root_window)
+    return;
+
+  keyboard::KeyboardController* const keyboard_controller =
+      keyboard::KeyboardController::GetInstance();
+  if (keyboard_activated &&
+      !keyboard_observer->IsObserving(keyboard_controller)) {
+    keyboard_observer->Add(keyboard_controller);
+  } else if (!keyboard_activated &&
+             keyboard_observer->IsObserving(keyboard_controller)) {
+    keyboard_observer->Remove(keyboard_controller);
+  }
+}
+
+}  // namespace ash