Release mouse pointer capture when it starts drag

third_party/WebKit/Source/core/input/PointerEventManager.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/PointerEventManager.h"
 
 #include "core/dom/ElementTraversal.h"
 #include "core/dom/FlatTreeTraversal.h"
 #include "core/dom/UserGestureIndicator.h"
 #include "core/events/MouseEvent.h"
@@ skipping 472 matching lines @@
     // Sending the leave/out events and lostpointercapture because the next
     // touch event will have a different id.
     ProcessCaptureAndPositionOfPointerEvent(pointer_event, nullptr);
 
     RemovePointer(pointer_event);
   }
 
   return result;
 }
 
+WebInputEventResult PointerEventManager::HandlePointerEvent(
+    const WebPointerEvent& web_pointer_event,
+    Node* target) {
+  // TODO(crbug.com/625841): This function only handles pointercancel for now.
+  // But we should extend it to handle any pointerevents.
+  DCHECK(web_pointer_event.GetType() == WebInputEvent::Type::kPointerCancel);

[dtapuska, 2017/07/13 19:21:36]

DCHECK_EQ is preferred

+  PointerEvent* pointer_event =
+      pointer_event_factory_.CreatePointerCancelEvent(web_pointer_event);
+
+  EventTarget* effective_target =
+      GetEffectiveTargetForPointerEvent(target, pointer_event->pointerId());
+  WebInputEventResult result =
+      DispatchPointerEvent(effective_target, pointer_event);
+
+  ReleasePointerCapture(pointer_event->pointerId());
+
+  // TODO(nzolghadr): Instead of |ProcessPendingPointerCapture| maybe we
+  // should have used ProcessCaptureAndPositionOfPointerEvent but that might
+  // be sending boundary events however we probably not want that all the
+  // time.
+  ProcessPendingPointerCapture(pointer_event);
+
+  RemovePointer(pointer_event);
+  return result;
+}
+
 WebInputEventResult PointerEventManager::SendMousePointerEvent(
     Node* target,
     const String& canvas_region_id,
     const AtomicString& mouse_event_type,
     const WebMouseEvent& mouse_event,
     const Vector<WebMouseEvent>& coalesced_events) {
   PointerEvent* pointer_event = pointer_event_factory_.Create(
       mouse_event_type, mouse_event, coalesced_events,
       frame_->GetDocument()->domWindow());
 
@@ skipping 279 matching lines @@
     if (first_id > unique_touch_event_id)
       return false;
     touch_ids_for_canceled_pointerdowns_.TakeFirst();
     if (first_id == unique_touch_event_id)
       return true;
   }
   return false;
 }
 
 }  // namespace blink