ash: Start/stop observing KeyboardController via ShellObserver

ash/root_window_controller.cc

Index: ash/root_window_controller.cc
diff --git a/ash/root_window_controller.cc b/ash/root_window_controller.cc
index 87b54b4cbf33f33bf10761afdffb2924e751f28a..2161d64af71c99bec53890ef5b443e81891c6baa 100644
--- a/ash/root_window_controller.cc
+++ b/ash/root_window_controller.cc
@@ -673,18 +673,15 @@ void RootWindowController::ActivateKeyboard(
     return;
   }
   DCHECK(keyboard_controller);
-  keyboard_controller->AddObserver(wm_shelf_->shelf_layout_manager());
-  keyboard_controller->AddObserver(panel_layout_manager());
-  keyboard_controller->AddObserver(docked_window_layout_manager());
-  keyboard_controller->AddObserver(workspace_controller()->layout_manager());
-  keyboard_controller->AddObserver(
-      always_on_top_controller_->GetLayoutManager());
-  Shell::GetInstance()->NotifyVirtualKeyboardActivated(true);
   aura::Window* parent = GetContainer(kShellWindowId_ImeWindowParentContainer);
   DCHECK(parent);
   aura::Window* keyboard_container = keyboard_controller->GetContainerWindow();
   keyboard_container->set_id(kShellWindowId_VirtualKeyboardContainer);
   parent->AddChild(keyboard_container);
+  // Notify observers after adding keyboard container because various layout
+  // managers are using the root window of the container window to decide
+  // whether the keyboard is relevant to them.
+  Shell::GetInstance()->NotifyVirtualKeyboardActivated(true);
 }
 
 void RootWindowController::DeactivateKeyboard(
@@ -702,15 +699,11 @@ void RootWindowController::DeactivateKeyboard(
     // keyboard before removing it from view hierarchy.
     keyboard_controller->HideKeyboard(
         keyboard::KeyboardController::HIDE_REASON_AUTOMATIC);
-    parent->RemoveChild(keyboard_container);
-    keyboard_controller->RemoveObserver(wm_shelf_->shelf_layout_manager());
-    keyboard_controller->RemoveObserver(panel_layout_manager());
-    keyboard_controller->RemoveObserver(docked_window_layout_manager());
-    keyboard_controller->RemoveObserver(
-        workspace_controller()->layout_manager());
-    keyboard_controller->RemoveObserver(
-        always_on_top_controller_->GetLayoutManager());
+    // Notify observers before removing keyboard container because various
+    // layout managers are using the root window of the container window to
+    // decide whether the keyboard is relevant to them.
     Shell::GetInstance()->NotifyVirtualKeyboardActivated(false);
+    parent->RemoveChild(keyboard_container);
   }
 }