Drop event should generate user gesture.

Source/web/WebViewImpl.cpp

Index: Source/web/WebViewImpl.cpp
diff --git a/Source/web/WebViewImpl.cpp b/Source/web/WebViewImpl.cpp
index 5975d51d80a5bee4ce4d586e26ec33523b84eebf..b6d85d24f5086f499c7327433cc3433d32aee770 100644
--- a/Source/web/WebViewImpl.cpp
+++ b/Source/web/WebViewImpl.cpp
@@ -136,6 +136,7 @@
 #include "platform/PlatformWheelEvent.h"
 #include "platform/PopupMenuClient.h"
 #include "platform/TraceEvent.h"
+#include "platform/UserGestureIndicator.h"
 #include "platform/exported/WebActiveGestureAnimation.h"
 #include "platform/fonts/FontCache.h"
 #include "platform/graphics/Color.h"
@@ -3168,6 +3169,7 @@ void WebViewImpl::dragTargetDrop(const WebPoint& clientPoint,
         screenPoint,
         static_cast<DragOperation>(m_operationsAllowed));
 
+    UserGestureIndicator gesture(DefinitelyProcessingNewUserGesture);
     m_page->dragController().performDrag(&dragData);
 
     m_dragOperation = WebDragOperationNone;