Release mouse pointer capture when it starts drag

third_party/WebKit/Source/core/input/MouseEventManager.cpp

 // Copyright 2016 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 "core/input/MouseEventManager.h"
 
 #include "core/clipboard/DataObject.h"
 #include "core/clipboard/DataTransfer.h"
 #include "core/dom/Element.h"
 #include "core/dom/ElementTraversal.h"
@@ skipping 855 matching lines @@
   }
 
   // Once we're past the drag threshold, we don't want to treat this gesture as
   // a click.
   InvalidateClick();
 
   if (!TryStartDrag(event)) {
     // Something failed to start the drag, clean up.
     ClearDragDataTransfer();
     ResetDragState();
+  } else {
+    // Since drag operation started we need to send a pointercancel for the
+    // corresponding pointer.
+    if (initiator == DragInitiator::kMouse) {
+      frame_->GetEventHandler().HandlePointerEvent(
+          WebPointerEvent(WebInputEvent::Type::kPointerCancel, event.Event()),
+          event.InnerNode());
+    }
+    // TODO(crbug.com/708278): If the drag starts with touch the touch cancel
+    // should trigger the release of pointer capture.
   }
 
   mouse_down_may_start_drag_ = false;
   // Whether or not the drag actually started, no more default handling (like
   // selection).
   return true;
 }
 
 DataTransfer* MouseEventManager::CreateDraggingDataTransfer() const {
   return DataTransfer::Create(DataTransfer::kDragAndDrop, kDataTransferWritable,
@@ skipping 205 matching lines @@
 
 void MouseEventManager::SetClickCount(int click_count) {
   click_count_ = click_count;
 }
 
 bool MouseEventManager::MouseDownMayStartDrag() {
   return mouse_down_may_start_drag_;
 }
 
 }  // namespace blink