Release mouse pointer capture when it starts drag

third_party/WebKit/public/platform/WebPointerEvent.h

 // Copyright 2017 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.
 
 #ifndef WebPointerEvent_h
 #define WebPointerEvent_h
 
 #include "WebInputEvent.h"
+#include "WebMouseEvent.h"
 #include "WebPointerProperties.h"
 #include "WebTouchEvent.h"
 
 namespace blink {
 
 // See WebInputEvent.h for details why this pack is here.
 #pragma pack(push, 4)
 
 // WebPointerEvent
 // This is a WIP and currently used only in Blink and only for touch.
 // TODO(nzolghadr): We should unify the fields in this class into
 // WebPointerProperties and not have pointertype specific attributes here.
 // --------------------------------------------------------------
 
 class WebPointerEvent : public WebInputEvent, public WebPointerProperties {
  public:
   WebPointerEvent()
       : WebInputEvent(sizeof(WebPointerEvent)), WebPointerProperties(0) {}
   BLINK_PLATFORM_EXPORT WebPointerEvent(const WebTouchEvent&,
                                         const WebTouchPoint&);
+  BLINK_PLATFORM_EXPORT WebPointerEvent(WebInputEvent::Type,
+                                        const WebMouseEvent&);
 
   // TODO(crbug.com/736014): We need a clarified definition of the scale and
   // the coordinate space on these attributes.
   float width;
   float height;
 
   // ------------ Touch Point Specific ------------
 
   float rotation_angle;
 
@@ skipping 18 matching lines @@
   BLINK_PLATFORM_EXPORT WebPointerEvent WebPointerEventInRootFrame() const;
 
 #endif
 };
 
 #pragma pack(pop)
 
 }  // namespace blink
 
 #endif  // WebMouseEvent_h