Release mouse pointer capture when it starts drag

third_party/WebKit/public/platform/WebPointerEvent.h

Index: third_party/WebKit/public/platform/WebPointerEvent.h
diff --git a/third_party/WebKit/public/platform/WebPointerEvent.h b/third_party/WebKit/public/platform/WebPointerEvent.h
index ef0606197dea30d59862ad7b1b395cc847b01e68..faf1213612efec1eb493334fe76b6e5e446fcf0e 100644
--- a/third_party/WebKit/public/platform/WebPointerEvent.h
+++ b/third_party/WebKit/public/platform/WebPointerEvent.h
@@ -6,6 +6,7 @@
 #define WebPointerEvent_h
 
 #include "WebInputEvent.h"
+#include "WebMouseEvent.h"
 #include "WebPointerProperties.h"
 #include "WebTouchEvent.h"
 
@@ -26,6 +27,7 @@ class WebPointerEvent : public WebInputEvent, public WebPointerProperties {
       : WebInputEvent(sizeof(WebPointerEvent)), WebPointerProperties(0) {}
   BLINK_PLATFORM_EXPORT WebPointerEvent(const WebTouchEvent&,
                                         const WebTouchPoint&);
+  BLINK_PLATFORM_EXPORT WebPointerEvent(const WebMouseEvent&, bool is_cancel);
 
   // TODO(crbug.com/736014): We need a clarified definition of the scale and
   // the coordinate space on these attributes.