mus: Implement interwindow drag and drop

services/ui/ws/window_server.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_server.h"
 
 #include <set>
 #include <string>
 
 #include "base/logging.h"
@@ skipping 466 matching lines @@
     return current_move_loop_->initiator;
   return nullptr;
 }
 
 gfx::Rect WindowServer::GetCurrentMoveLoopRevertBounds() {
   if (current_move_loop_)
     return current_move_loop_->revert_bounds;
   return gfx::Rect();
 }
 
+void WindowServer::StartDragLoop(uint32_t change_id) {
+  current_drag_loop_ = change_id;
+}
+
+void WindowServer::EndDragLoop() {
+  current_drag_loop_.reset();
+}
+
+uint32_t WindowServer::GetCurrentDragLoopChangeId() {
+  return current_drag_loop_.value_or(0u);
+}
+
 bool WindowServer::GetAndClearInFlightWindowManagerChange(
     uint32_t window_manager_change_id,
     InFlightWindowManagerChange* change) {
   // There are valid reasons as to why we wouldn't know about the id. The
   // most likely is the client disconnected before the response from the window
   // manager came back.
   auto iter = in_flight_wm_change_map_.find(window_manager_change_id);
   if (iter == in_flight_wm_change_map_.end())
     return false;
 
@@ skipping 285 matching lines @@
   clipboard_map_[id] = base::MakeUnique<clipboard::ClipboardImpl>();
 }
 
 void WindowServer::OnUserIdRemoved(const UserId& id) {
   activity_monitor_map_.erase(id);
   clipboard_map_.erase(id);
 }
 
 }  // namespace ws
 }  // namespace ui