Current work-in-progress crbug.com/567021

third_party/WebKit/Source/core/css/StyleSheetContents.cpp

Index: third_party/WebKit/Source/core/css/StyleSheetContents.cpp
diff --git a/third_party/WebKit/Source/core/css/StyleSheetContents.cpp b/third_party/WebKit/Source/core/css/StyleSheetContents.cpp
index c79583017a736b1fbbab801410603b05f9e01ebe..24326c5553ce7ebc5e92576df644bb8d8c68373d 100644
--- a/third_party/WebKit/Source/core/css/StyleSheetContents.cpp
+++ b/third_party/WebKit/Source/core/css/StyleSheetContents.cpp
@@ -274,7 +274,9 @@ bool StyleSheetContents::wrapperInsertRule(StyleRuleBase* rule, unsigned index)
     if (rule->isMediaRule())
         setHasMediaQueries();
     else if (rule->isFontFaceRule())
-        setHasFontFaceRule(true);
+        setHasFontFaceRule();
+    else if (rule->isViewportRule())
+        setHasViewportRule();
 
     m_childRules.insert(index, rule);
     return true;
@@ -608,11 +610,21 @@ RuleSet& StyleSheetContents::ensureRuleSet(const MediaQueryEvaluator& medium, Ad
     return *m_ruleSet.get();
 }
 
-static void clearResolvers(HeapHashSet<WeakMember<CSSStyleSheet>>& clients)
+RuleSet& StyleSheetContents::ensureEmptyRuleSet()
+{
+    DCHECK(m_ruleSet);
+    m_ruleSet = RuleSet::create();
+    return *m_ruleSet.get();
+}
+
+static void setNeedsActiveStyleUpdateForClients(HeapHashSet<WeakMember<CSSStyleSheet>>& clients)
 {
     for (const auto& sheet : clients) {
-        if (Document* document = sheet->ownerDocument())
-            document->styleEngine().clearResolver();
+        Document* document = sheet->ownerDocument();
+        Node* node = sheet->ownerNode();
+        if (!document || !node || !node->inShadowIncludingDocument())
+            continue;
+        document->styleEngine().setNeedsActiveStyleUpdate(node->treeScope());
     }
 }
 
@@ -621,17 +633,13 @@ void StyleSheetContents::clearRuleSet()
     if (StyleSheetContents* parentSheet = parentStyleSheet())
         parentSheet->clearRuleSet();
 
-    // Don't want to clear the StyleResolver if the RuleSet hasn't been created
-    // since we only clear the StyleResolver so that it's members are properly
-    // updated in ScopedStyleResolver::addRulesFromSheet.
     if (!m_ruleSet)
         return;
 
-    // Clearing the ruleSet means we need to recreate the styleResolver data structures.
-    // See the StyleResolver calls in ScopedStyleResolver::addRulesFromSheet.
-    clearResolvers(m_loadingClients);
-    clearResolvers(m_completedClients);
     m_ruleSet.clear();
+
+    setNeedsActiveStyleUpdateForClients(m_loadingClients);
+    setNeedsActiveStyleUpdateForClients(m_completedClients);
 }
 
 static void removeFontFaceRules(HeapHashSet<WeakMember<CSSStyleSheet>>& clients, const StyleRuleFontFace* fontFaceRule)