Remove docked windows entirely in M59.

ash/root_window_controller.h

Index: ash/root_window_controller.h
diff --git a/ash/root_window_controller.h b/ash/root_window_controller.h
index a838bfc30a4490eef72605e186a462c0af549583..0f0cc08b343decd0bbe44ff9a5718f4ffbaa5225 100644
--- a/ash/root_window_controller.h
+++ b/ash/root_window_controller.h
@@ -51,7 +51,6 @@ class AnimatingWallpaperWidgetController;
 class AshTouchExplorationManager;
 class AshWindowTreeHost;
 class BootSplashScreen;
-class DockedWindowLayoutManager;
 enum class LoginStatus;
 class PanelLayoutManager;
 class ShelfLayoutManager;
@@ -162,10 +161,6 @@ class ASH_EXPORT RootWindowController : public ShellObserver {
     touch_hud_projection_ = hud;
   }
 
-  DockedWindowLayoutManager* docked_window_layout_manager() {
-    return docked_window_layout_manager_;
-  }
-
   PanelLayoutManager* panel_layout_manager() { return panel_layout_manager_; }
 
   wm::RootWindowLayoutManager* root_window_layout_manager() {
@@ -337,7 +332,6 @@ class ASH_EXPORT RootWindowController : public ShellObserver {
   aura::WindowTreeHost* window_tree_host_;
 
   // LayoutManagers are owned by the window they are installed on.
-  DockedWindowLayoutManager* docked_window_layout_manager_ = nullptr;
   PanelLayoutManager* panel_layout_manager_ = nullptr;
   wm::RootWindowLayoutManager* root_window_layout_manager_ = nullptr;