Add fast-path for propagated variable changes (WIP)

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc.
  * All rights reserved.
  *           (C) 2007 Eric Seidel (eric@webkit.org)
  *
@@ skipping 1879 matching lines @@
     clearChildNeedsStyleRecalc();
     clearChildNeedsReattachLayoutTree();
   }
 
   if (hasCustomStyleCallbacks())
     didRecalcStyle(change);
 }
 
 PassRefPtr<ComputedStyle> Element::propagateInheritedProperties(
     StyleRecalcChange change) {
-  if (change != IndependentInherit)
+  if (change != IndependentInherit && change != IndependentInheritWithVariables)
     return nullptr;
   if (isPseudoElement())
     return nullptr;
   if (needsStyleRecalc())
     return nullptr;
   if (hasAnimations())
     return nullptr;
   const ComputedStyle* parentStyle = parentComputedStyle();
   DCHECK(parentStyle);
   const ComputedStyle* style = computedStyle();
   if (!style || style->animations() || style->transitions())
     return nullptr;
+  if (change == IndependentInheritWithVariables &&
+      (style->hasVariableReferenceFromInheritedProperty() ||
+       style->hasVariableReferenceFromNonInheritedProperty()
+       // If this element sets any variables, they may refer to other variables.
+       // To be safe, recalc the element's style.
+       // TODO(sashab): Set the hasVariableReferenceFromInheritedProperty flag
+       // on ComputedStyle when a variable references another variable and
+       // remove this additional check.
+       || style->hasAnyNonInheritedVariableDefinitions()))
+    return nullptr;
   RefPtr<ComputedStyle> newStyle = ComputedStyle::clone(*style);
   newStyle->propagateIndependentInheritedProperties(*parentStyle);
   INCREMENT_STYLE_STATS_COUNTER(document().styleEngine(),
                                 independentInheritedStylesPropagated, 1);
   return newStyle;
 }
 
 StyleRecalcChange Element::recalcOwnStyle(StyleRecalcChange change,
                                           Text* nextTextSibling) {
   DCHECK(document().inStyleRecalc());
@@ skipping 12 matching lines @@
   DCHECK(newStyle);
 
   StyleRecalcChange localChange =
       ComputedStyle::stylePropagationDiff(oldStyle.get(), newStyle.get());
   if (localChange == NoChange) {
     INCREMENT_STYLE_STATS_COUNTER(document().styleEngine(), stylesUnchanged, 1);
   } else {
     INCREMENT_STYLE_STATS_COUNTER(document().styleEngine(), stylesChanged, 1);
   }
 
+  if (change == IndependentInheritWithVariables && localChange == NoChange) {
+    // If we are in a propagation fast-path, but we have changed variables,
+    // there
+    // might still be properties that need to be updated below. Force continue.
+    localChange = IndependentInheritWithVariables;
+  }
+
   if (localChange == Reattach) {
     StyleReattachData styleReattachData;
     styleReattachData.computedStyle = std::move(newStyle);
     styleReattachData.nextTextSibling = nextTextSibling;
     document().addStyleReattachData(*this, styleReattachData);
     setNeedsReattachLayoutTree();
     return rebuildLayoutTree();
   }
 
   DCHECK(oldStyle);
@@ skipping 2134 matching lines @@
 }
 
 DEFINE_TRACE_WRAPPERS(Element) {
   if (hasRareData()) {
     visitor->traceWrappers(elementRareData());
   }
   ContainerNode::traceWrappers(visitor);
 }
 
 }  // namespace blink