Drop event should generate user gesture.

Source/web/WebViewImpl.cpp

 /*
  * Copyright (C) 2011, 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 118 matching lines @@
 #include "platform/Cursor.h"
 #include "platform/KeyboardCodes.h"
 #include "platform/NotImplemented.h"
 #include "platform/OverscrollTheme.h"
 #include "platform/PlatformGestureEvent.h"
 #include "platform/PlatformKeyboardEvent.h"
 #include "platform/PlatformMouseEvent.h"
 #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"
 #include "platform/graphics/Image.h"
 #include "platform/graphics/ImageBuffer.h"
 #include "platform/scroll/ScrollbarTheme.h"
 #include "platform/weborigin/SchemeRegistry.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebDragData.h"
 #include "public/platform/WebFloatPoint.h"
@@ skipping 3012 matching lines @@
         return;
     }
 
     m_currentDragData->setModifierKeyState(webInputEventKeyStateToPlatformEventKeyState(keyModifiers));
     DragData dragData(
         m_currentDragData.get(),
         clientPoint,
         screenPoint,
         static_cast<DragOperation>(m_operationsAllowed));
 
+    UserGestureIndicator gesture(DefinitelyProcessingNewUserGesture);
     m_page->dragController().performDrag(&dragData);
 
     m_dragOperation = WebDragOperationNone;
     m_currentDragData = nullptr;
 }
 
 void WebViewImpl::spellingMarkers(WebVector<uint32_t>* markers)
 {
     Vector<uint32_t> result;
     for (LocalFrame* frame = m_page->mainFrame(); frame; frame = frame->tree().traverseNext()) {
@@ skipping 814 matching lines @@
     const PageScaleConstraints& constraints = m_pageScaleConstraintsSet.pageDefinedConstraints();
 
     if (!mainFrameImpl() || !mainFrameImpl()->frameView())
         return false;
 
     return mainFrameImpl()->frameView()->layoutSize().width() == m_size.width
         || (constraints.minimumScale == constraints.maximumScale && constraints.minimumScale != -1);
 }
 
 } // namespace blink