Use weak members to cache StyleSheetContents.

third_party/WebKit/Source/core/dom/StyleEngine.cpp

Index: third_party/WebKit/Source/core/dom/StyleEngine.cpp
diff --git a/third_party/WebKit/Source/core/dom/StyleEngine.cpp b/third_party/WebKit/Source/core/dom/StyleEngine.cpp
index f739839f9b39e6d90d334df236eb63c7d8c3ba62..a5fb3f8c7d5933fb1afeddb52218f55d312c65da 100644
--- a/third_party/WebKit/Source/core/dom/StyleEngine.cpp
+++ b/third_party/WebKit/Source/core/dom/StyleEngine.cpp
@@ -511,18 +511,20 @@ CSSStyleSheet* StyleEngine::createSheet(Element* e, const String& text, TextPosi
 
     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);
     }
 
@@ -541,16 +543,6 @@ CSSStyleSheet* StyleEngine::parseSheet(Element* e, const String& text, TextPosit
     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;