Use weak members to cache StyleSheetContents.

third_party/WebKit/Source/core/dom/StyleEngine.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, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 493 matching lines @@
 }
 
 CSSStyleSheet* StyleEngine::createSheet(Element* e, const String& text, TextPosition startPosition, StyleEngineContext &context)
 {
     CSSStyleSheet* styleSheet = nullptr;
 
     e->document().styleEngine().addPendingSheet(context);
 
     AtomicString textContent(text);
 
-    HeapHashMap<AtomicString, Member<StyleSheetContents>>::AddResult result = m_textToSheetCache.add(textContent, nullptr);
-    if (result.isNewEntry || !result.storedValue->value) {
+    auto result = m_textToSheetCache.add(textContent, nullptr);
+    StyleSheetContents* contents = result.storedValue->value;
+    if (result.isNewEntry || !contents || !contents->isCacheableForStyleElement()) {
+        result.storedValue->value = nullptr;
         styleSheet = StyleEngine::parseSheet(e, text, startPosition);
-        if (result.isNewEntry && styleSheet->contents()->isCacheableForStyleElement()) {
+        if (styleSheet->contents()->isCacheableForStyleElement()) {
             result.storedValue->value = styleSheet->contents();
             m_sheetToTextCache.add(styleSheet->contents(), textContent);
         }
     } else {
-        StyleSheetContents* contents = result.storedValue->value;
         DCHECK(contents);
         DCHECK(contents->isCacheableForStyleElement());
-        DCHECK_EQ(contents->singleOwnerDocument(), e->document());
+        DCHECK(contents->hasSingleOwnerDocument());
+        contents->setIsUsedFromTextCache();
         styleSheet = CSSStyleSheet::createInline(contents, e, startPosition);
     }
 
     DCHECK(styleSheet);
     styleSheet->setTitle(e->title());
     if (!e->isInShadowTree())
         setPreferredStylesheetSetNameIfNotSet(e->title());
     return styleSheet;
 }
 
 CSSStyleSheet* StyleEngine::parseSheet(Element* e, const String& text, TextPosition startPosition)
 {
     CSSStyleSheet* styleSheet = nullptr;
     styleSheet = CSSStyleSheet::createInline(e, KURL(), startPosition, e->document().characterSet());
     styleSheet->contents()->parseStringAtPosition(text, startPosition);
     return styleSheet;
 }
 
-void StyleEngine::removeSheet(StyleSheetContents* contents)
-{
-    HeapHashMap<Member<StyleSheetContents>, AtomicString>::iterator it = m_sheetToTextCache.find(contents);
-    if (it == m_sheetToTextCache.end())
-        return;
-
-    m_textToSheetCache.remove(it->value);
-    m_sheetToTextCache.remove(contents);
-}
-
 void StyleEngine::collectScopedStyleFeaturesTo(RuleFeatureSet& features) const
 {
     HeapHashSet<Member<const StyleSheetContents>> visitedSharedStyleSheetContents;
     if (document().scopedStyleResolver())
         document().scopedStyleResolver()->collectFeaturesTo(features, visitedSharedStyleSheetContents);
     for (TreeScope* treeScope : m_activeTreeScopes) {
         // When creating StyleResolver, dirty treescopes might not be processed.
         // So some active treescopes might not have a scoped style resolver.
         // In this case, we should skip collectFeatures for the treescopes without
         // scoped style resolvers. When invoking updateActiveStyleSheets,
@@ skipping 265 matching lines @@
 
 DEFINE_TRACE_WRAPPERS(StyleEngine)
 {
     for (auto sheet : m_injectedAuthorStyleSheets) {
         visitor->traceWrappers(sheet);
     }
     visitor->traceWrappers(m_documentStyleSheetCollection);
 }
 
 } // namespace blink