Store a single inspector stylesheet hidden from CSSOM.

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)
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
@@ skipping 60 matching lines @@
         if (candidate.canBeActivated(engine.preferredStylesheetSetName()))
             collector.appendActiveStyleSheet(toCSSStyleSheet(sheet));
     }
 }
 
 void DocumentStyleSheetCollection::collectStyleSheets(StyleEngine& engine, DocumentStyleSheetCollector& collector)
 {
     DCHECK_EQ(&document().styleEngine(), &engine);
     collector.appendActiveStyleSheets(engine.injectedAuthorStyleSheets());
     collectStyleSheetsFromCandidates(engine, collector);
+    if (engine.inspectorStyleSheet())
+        collector.appendActiveStyleSheet(engine.inspectorStyleSheet());
 }
 
 void DocumentStyleSheetCollection::updateActiveStyleSheets(StyleEngine& engine, StyleResolverUpdateMode updateMode)
 {
     // StyleSheetCollection is GarbageCollected<>, allocate it on the heap.
     StyleSheetCollection* collection = StyleSheetCollection::create();
     ActiveDocumentStyleSheetCollector collector(*collection);
     collectStyleSheets(engine, collector);
 
     StyleSheetChange change;
@@ skipping 25 matching lines @@
     collection->dispose();
 }
 
 DEFINE_TRACE_WRAPPERS(DocumentStyleSheetCollection)
 {
     for (auto sheet : m_styleSheetsForStyleSheetList) {
         visitor->traceWrappers(sheet);
     }
 }
 } // namespace blink