Speculative fix for crash in blink::WebFrameWidgetBase::dragTargetDragEnterOrOver

third_party/WebKit/Source/web/WebFrameWidgetBase.cpp

Index: third_party/WebKit/Source/web/WebFrameWidgetBase.cpp
diff --git a/third_party/WebKit/Source/web/WebFrameWidgetBase.cpp b/third_party/WebKit/Source/web/WebFrameWidgetBase.cpp
index 79e51fc74f47f7e990c4f1dec0e24542238a19db..b9139dc30dec1ac97a37cc9e4ec9f21297ec093a 100644
--- a/third_party/WebKit/Source/web/WebFrameWidgetBase.cpp
+++ b/third_party/WebKit/Source/web/WebFrameWidgetBase.cpp
@@ -177,7 +177,12 @@ WebDragOperation WebFrameWidgetBase::dragTargetDragEnterOrOver(
     DragAction dragAction,
     int modifiers) {
   DCHECK(m_currentDragData);
-  if (ignoreInputEvents()) {
+  // TODO(paulmeyer): It shouldn't be possible for |m_currentDragData| to be
+  // null here, but this is somehow happening (rarely). This suggests that in
+  // some cases drag-over is happening before drag-enter, which should be
+  // impossible. This needs to be investigated further. Once fixed, the extra
+  // check for |!m_currentDragData| should be removed. (crbug.com/671504)
+  if (ignoreInputEvents() || !m_currentDragData) {
     cancelDrag();
     return WebDragOperationNone;
   }