exo: Fix dragging regression

components/exo/shell_surface.cc

 // Copyright 2015 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 "components/exo/shell_surface.h"
 
 #include <algorithm>
 
 #include "ash/frame/custom_frame_view_ash.h"
 #include "ash/public/cpp/shelf_types.h"
@@ skipping 1251 matching lines @@
       << "Number of pending configure acks for shell surface has reached: "
       << pending_configs_.size();
 }
 
 aura::Window* ShellSurface::GetDragWindow() {
   switch (bounds_mode_) {
     case BoundsMode::SHELL:
       return widget_->GetNativeWindow();
 
     case BoundsMode::CLIENT:
-      return host_window();
+      return root_surface() ? root_surface()->window() : nullptr;
 
     case BoundsMode::FIXED:
       return nullptr;
   }
 
   NOTREACHED();
   return nullptr;
 }
 
 void ShellSurface::AttemptToStartDrag(int component) {
@@ skipping 398 matching lines @@
 gfx::Point ShellSurface::GetMouseLocation() const {
   aura::Window* const root_window = widget_->GetNativeWindow()->GetRootWindow();
   gfx::Point location =
       root_window->GetHost()->dispatcher()->GetLastMouseLocationInRoot();
   aura::Window::ConvertPointToTarget(
       root_window, widget_->GetNativeWindow()->parent(), &location);
   return location;
 }
 
 }  // namespace exo