mus drag and drop: Add API to let the client cancel the drag.

services/ui/ws/window_tree.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_tree.h"
 
 #include <stddef.h>
 
 #include <utility>
 
@@ skipping 1528 matching lines @@
 
   // Here, we need to dramatically change how the mouse pointer works. Once
   // we've started a drag drop operation, cursor events don't go to windows as
   // normal.
   WindowManagerState* wms = display_root->window_manager_state();
   window_server_->StartDragLoop(change_id, window, this);
   wms->SetDragDropSourceWindow(this, window, this, drag_pointer,
                                std::move(drag_data), drag_operation);
 }
 
+void WindowTree::CancelDragDrop(Id window_id) {
+  ServerWindow* window = GetWindowByClientId(ClientWindowId(window_id));
+  if (!window) {
+    DVLOG(1) << "CancelDragDrop failed (no window)";
+    return;
+  }
+
+  if (window != window_server_->GetCurrentDragLoopWindow()) {
+    DVLOG(1) << "CancelDragDrop failed (not the drag loop window)";
+    return;
+  }
+
+  if (window_server_->GetCurrentDragLoopInitiator() != this) {
+    DVLOG(1) << "CancelDragDrop failed (not the drag initiator)";
+    return;
+  }
+
+  WindowManagerDisplayRoot* display_root = GetWindowManagerDisplayRoot(window);
+  if (!display_root) {
+    DVLOG(1) << "CancelDragDrop failed (no such window manager display root)";
+    return;
+  }
+
+  WindowManagerState* wms = display_root->window_manager_state();
+  wms->CancelDragDrop();
+}
+
 void WindowTree::PerformWindowMove(uint32_t change_id,
                                    Id window_id,
                                    ui::mojom::MoveLoopSource source,
                                    const gfx::Point& cursor) {
   ServerWindow* window = GetWindowByClientId(ClientWindowId(window_id));
   bool success = window && access_policy_->CanInitiateMoveLoop(window);
   if (!success || !ShouldRouteToWindowManager(window)) {
     // We need to fail this move loop change, otherwise the client will just be
     // waiting for |change_id|.
     DVLOG(1) << "PerformWindowMove failed (access denied).";
@@ skipping 29 matching lines @@
       window_server_->GenerateWindowManagerChangeId(this, change_id);
   window_server_->StartMoveLoop(wm_change_id, window, this, window->bounds());
   wms->window_tree()->window_manager_internal_->WmPerformMoveLoop(
       wm_change_id, wms->window_tree()->ClientWindowIdForWindow(window).id,
       source, cursor);
 }
 
 void WindowTree::CancelWindowMove(Id window_id) {
   ServerWindow* window = GetWindowByClientId(ClientWindowId(window_id));
   bool success = window && access_policy_->CanInitiateMoveLoop(window);
-  if (!success)
+  if (!success) {
+    DVLOG(1) << "CancelWindowMove failed (no window / access denied)";
     return;
+  }
 
-  if (window != window_server_->GetCurrentMoveLoopWindow())
+  if (window != window_server_->GetCurrentMoveLoopWindow()) {
+    DVLOG(1) << "CancelWindowMove failed (not the move loop window)";
     return;
+  }
 
-  if (window_server_->GetCurrentMoveLoopInitiator() != this)
+  if (window_server_->GetCurrentMoveLoopInitiator() != this) {
+    DVLOG(1) << "CancelWindowMove failed (not the move loop initiator)";
     return;
+  }
 
   WindowManagerDisplayRoot* display_root = GetWindowManagerDisplayRoot(window);
-  if (!display_root)
+  if (!display_root) {
+    DVLOG(1) << "CancelWindowMove failed (no such window manager display root)";
     return;
+  }
 
   WindowManagerState* wms = display_root->window_manager_state();
   wms->window_tree()->window_manager_internal_->WmCancelMoveLoop(
       window_server_->GetCurrentMoveLoopChangeId());
 }
 
 void WindowTree::AddAccelerator(uint32_t id,
                                 mojom::EventMatcherPtr event_matcher,
                                 const AddAcceleratorCallback& callback) {
   DCHECK(window_manager_state_);
@@ skipping 252 matching lines @@
   client()->OnCompleteDrop(client_window_id.id, event_flags, cursor_offset,
                            effect_bitmask, callback);
 }
 
 void WindowTree::PerformOnDragDropDone() {
   client()->OnDragDropDone();
 }
 
 }  // namespace ws
 }  // namespace ui