ash: Start/stop observing KeyboardController via ShellObserver

ash/shell.cc

Index: ash/shell.cc
diff --git a/ash/shell.cc b/ash/shell.cc
index 95bf8f60a021f034c0d9a18665110674de43cf20..0167715d20db6b6f1087afa65f826b53ec0e22e0 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -455,9 +455,10 @@ void Shell::NotifyPinnedStateChanged(WmWindow* pinned_window) {
     observer.OnPinnedStateChanged(pinned_window);
 }
 
-void Shell::NotifyVirtualKeyboardActivated(bool activated) {
+void Shell::NotifyVirtualKeyboardActivated(bool activated,
+                                           WmWindow* root_window) {
   for (auto& observer : shell_observers_)
-    observer.OnVirtualKeyboardStateChanged(activated);
+    observer.OnVirtualKeyboardStateChanged(activated, root_window);
 }
 
 void Shell::NotifyShelfCreatedForRootWindow(WmWindow* root_window) {