Fix a document memory leak in drag-and-drop.

Source/core/page/EventHandler.cpp

Index: Source/core/page/EventHandler.cpp
diff --git a/Source/core/page/EventHandler.cpp b/Source/core/page/EventHandler.cpp
index 55a07108fe384eddf4e7d7407552417884a1d2ed..ea478dcd280abfa4f73b8c457aeaf16d9647ac70 100644
--- a/Source/core/page/EventHandler.cpp
+++ b/Source/core/page/EventHandler.cpp
@@ -3037,8 +3037,11 @@ bool EventHandler::dragHysteresisExceeded(const FloatPoint& dragViewportLocation
 
 void EventHandler::freeClipboard()
 {
-    if (dragState().m_dragClipboard)
+    if (dragState().m_dragClipboard) {
+        dragState().m_dragSrc = nullptr;

[haraken, 2014/05/30 12:35:29]

You'll need to move this to outside of the if branch. Then you can remove
"m_dragSrc = nullptr" after freeClipboard(), as kouhei-san suggested.

+        dragState().m_dragClipboard->clearDragImage();
         dragState().m_dragClipboard->setAccessPolicy(ClipboardNumb);
+    }
 }
 
 void EventHandler::dragSourceEndedAt(const PlatformMouseEvent& event, DragOperation operation)