Add more checks to diagnose MediaQuerySet issue

third_party/WebKit/Source/core/dom/DocumentStyleSheetCollection.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, 2012 Apple Inc. All
  * rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
@@ skipping 32 matching lines @@
     TreeScope& tree_scope)
     : TreeScopeStyleSheetCollection(tree_scope) {
   DCHECK_EQ(tree_scope.RootNode(), tree_scope.RootNode().GetDocument());
 }
 
 void DocumentStyleSheetCollection::CollectStyleSheetsFromCandidates(
     StyleEngine& master_engine,
     DocumentStyleSheetCollector& collector) {
   DocumentOrderedList::MutationForbiddenScope mutation_forbidden_(
       &style_sheet_candidate_nodes_);
+  // TODO(keishi) Check added for crbug.com/699269 diagnosis. Remove once done.
+  CHECK(HeapObjectHeader::FromPayload(this)->IsValid());
+  CHECK(ThreadState::Current()->IsOnThreadHeap(this));
   for (Node* n : style_sheet_candidate_nodes_) {
+    CHECK(HeapObjectHeader::FromPayload(n)->IsValid());
+    CHECK(ThreadState::Current()->IsOnThreadHeap(n));
     StyleSheetCandidate candidate(*n);
 
     DCHECK(!candidate.IsXSL());
     if (candidate.IsImport()) {
       Document* document = candidate.ImportedDocument();
       if (!document)
         continue;
       if (collector.HasVisited(document))
         continue;
       collector.WillVisit(document);
@@ skipping 59 matching lines @@
       continue;
     if (!candidate.CanBeActivated(
             GetDocument().GetStyleEngine().PreferredStylesheetSetName()))
       continue;
     viewport_resolver.CollectViewportRulesFromAuthorSheet(
         *ToCSSStyleSheet(sheet));
   }
 }
 
 }  // namespace blink