Merge r185896 - [GTK] Crash performing drag-and-drop

https://bugs.webkit.org/show_bug.cgi?id=146267

Reviewed by Darin Adler.

Return early if gtk_get_current_event() returns null to avoid a crash. Note that this does
not fix drag-and-drop. Note also this prevents the web process from forcing the UI process
to crash by sending fake startDrag messages.

* UIProcess/gtk/DragAndDropHandler.cpp:
(WebKit::DragAndDropHandler::startDrag):

Source/WebKit2/ChangeLog

@@ -1,3 +1,17 @@
+2015-06-23  Michael Catanzaro  <mcatanzaro@igalia.com>
+
+        [GTK] Crash performing drag-and-drop
+        https://bugs.webkit.org/show_bug.cgi?id=146267
+
+        Reviewed by Darin Adler.
+
+        Return early if gtk_get_current_event() returns null to avoid a crash. Note that this does
+        not fix drag-and-drop. Note also this prevents the web process from forcing the UI process
+        to crash by sending fake startDrag messages.
+
+        * UIProcess/gtk/DragAndDropHandler.cpp:
+        (WebKit::DragAndDropHandler::startDrag):
+
 2015-06-22  Gyuyoung Kim  <gyuyoung.kim@webkit.org>
 
         [EFL][CustomProtocol] Do not add duplicated custom scheme

Source/WebKit2/UIProcess/gtk/DragAndDropHandler.cpp

@@ -114,6 +114,9 @@ void DragAndDropHandler::startDrag(const DragData& dragData, PassRefPtr<Shareabl
     GRefPtr<GtkTargetList> targetList = adoptGRef(PasteboardHelper::defaultPasteboardHelper()->targetListForDataObject(dataObject.get()));
     GUniquePtr<GdkEvent> currentEvent(gtk_get_current_event());
 
+    if (!currentEvent)
+        return;
+
     GdkDragContext* context = gtk_drag_begin(m_page.viewWidget(), targetList.get(), dragOperationToGdkDragActions(dragData.draggingSourceOperationMask()),
         GDK_BUTTON_PRIMARY, currentEvent.get());
     m_draggingDataObjects.set(context, dataObject.get());