Fix bug causing DCHECKs to be hit in DocumentMarkerController

third_party/WebKit/Source/core/editing/markers/DocumentMarkerController.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights
  * reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
@@ skipping 77 matching lines @@
 
 Member<DocumentMarkerList>& DocumentMarkerController::ListForType(
     MarkerLists* marker_lists,
     DocumentMarker::MarkerType type) {
   const size_t marker_list_index = MarkerTypeToMarkerIndex(type);
   return (*marker_lists)[marker_list_index];
 }
 
 inline bool DocumentMarkerController::PossiblyHasMarkers(
     DocumentMarker::MarkerTypes types) {
+  if (markers_.IsEmpty()) {
+    // It's possible for markers_ to become empty through garbage collection if
+    // all its Nodes are GC'ed since we only hold weak references, in which case
+    // possibly_existing_marker_types_ isn't reset to 0 as it is in the other
+    // codepaths that remove from markers_. Therefore, we check for this case
+    // here.
+
+    // Alternatively, we could handle this case at the time the Node is GC'ed,
+    // but that operation is more performance-sensitive than anywhere
+    // PossiblyHasMarkers() is used.
+    possibly_existing_marker_types_ = 0;
+    return false;
+  }
+
   return possibly_existing_marker_types_.Intersects(types);
 }
 
 DocumentMarkerController::DocumentMarkerController(Document& document)
     : possibly_existing_marker_types_(0), document_(&document) {
   SetContext(&document);
 }
 
 void DocumentMarkerController::Clear() {
   markers_.clear();
@@ skipping 633 matching lines @@
 }
 
 }  // namespace blink
 
 #ifndef NDEBUG
 void showDocumentMarkers(const blink::DocumentMarkerController* controller) {
   if (controller)
     controller->ShowMarkers();
 }
 #endif