mus: Implement interwindow drag and drop

services/ui/ws/window_manager_access_policy.cc

 // Copyright 2014 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 "services/ui/ws/window_manager_access_policy.h"
 
 #include "services/ui/ws/access_policy_delegate.h"
 #include "services/ui/ws/server_window.h"
 
 namespace ui {
@@ skipping 120 matching lines @@
   return WasCreatedByThisClient(window) ||
          delegate_->HasRootForAccessPolicy(window);
 }
 
 bool WindowManagerAccessPolicy::CanSetHitTestMask(
     const ServerWindow* window) const {
   return WasCreatedByThisClient(window) ||
          delegate_->HasRootForAccessPolicy(window);
 }
 
+bool WindowManagerAccessPolicy::CanSetAcceptDrags(
+    const ServerWindow* window) const {
+  // Only the client associated with a window may set this.

[sky, 2016/09/06 21:11:27]

Are you sure you don't want WasCreatedByThisClient(window)? Otherwise it means
any windows created by the window manager can't accept drags.

+  return false;
+}
+
 bool WindowManagerAccessPolicy::CanSetAcceptEvents(
     const ServerWindow* window) const {
   return WasCreatedByThisClient(window) ||
          delegate_->HasRootForAccessPolicy(window);
 }
 
 bool WindowManagerAccessPolicy::CanSetCursorProperties(
     const ServerWindow* window) const {
   return WasCreatedByThisClient(window) ||
          delegate_->HasRootForAccessPolicy(window);
@@ skipping 39 matching lines @@
   return WindowIdFromTransportId(id.id).client_id == client_id_;
 }
 
 bool WindowManagerAccessPolicy::WasCreatedByThisClient(
     const ServerWindow* window) const {
   return window->id().client_id == client_id_;
 }
 
 }  // namespace ws
 }  // namespace ui