Implement style invalidation tree walk for targeted style recalc upon class change.

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index e3199112cca649bf8ae7e40a0ba871602fad2a2f..7f144d93b546cbd40144fe65999061faf261709f 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -1528,7 +1528,7 @@ PassRefPtr<TreeWalker> Document::createTreeWalker(Node* root, unsigned whatToSho
 
 bool Document::shouldCallRecalcStyleForDocument()
 {
-    return needsStyleRecalc() || childNeedsStyleRecalc() || childNeedsDistributionRecalc() || !m_useElementsNeedingUpdate.isEmpty();
+    return needsStyleRecalc() || childNeedsStyleRecalc() || childNeedsDistributionRecalc() || !m_useElementsNeedingUpdate.isEmpty() || childNeedsStyleInvalidation();
 }
 
 void Document::scheduleStyleRecalc()
@@ -1570,6 +1570,21 @@ void Document::updateDistributionIfNeeded()
     recalcDistribution();
 }
 
+void Document::updateStyleInvalidationIfNeeded()
+{
+    if (!childNeedsStyleInvalidation())
+        return;
+    TRACE_EVENT0("webkit", "Document::computeNeedsStyleRecalcState");
+    if (!styleResolver()) {
+        clearChildNeedsStyleInvalidation();

[ojan, 2014/01/29 00:50:07]

I think we still need to do the style invalidation walk even if there's no
styleResolver, no?

[chrishtr, 2014/01/29 01:56:42]

The style invalidation data structure lives in the styleResolver() object right
now, so either that is incorrect (even with the style resolver reset timer
removed), or the code is ok. Is it ok so long as the style resolver is never
cleared?

[ojan, 2014/01/29 02:00:25]

I see. Yeah, it seems like we have to block turning this flag on on getting rid
of the reset timer. Otherwise, you'll get in a situation where you don't do the
style invalidation in some cases and miss doing some recalcs you need to do,
right?

[chrishtr, 2014/01/29 02:02:32]

Yes. My plan is to try to land the change that removes the timer, but not block
this CL on that, since the code in this CL is behind a flag. If I can't get the
other change to land, I'll move the data for this CL elsewhere in a followup.

+        return;
+    }
+
+    // FIXME: the style resolver can be deleted at present. Either resolve
+    // crbug.com/335964 or move the invalidation data elsewhere.

[ojan, 2014/01/29 00:50:07]

You can use use ensureStyleResolver(). I don't see any problem with recreateding
the styleResolver here if it doesn't exist. You're going to need it right after
this to do the rest of the styleRecalc anyways.

[chrishtr, 2014/01/29 01:56:42]

See above.

+    styleResolver()->ensureRuleFeatureSet().computeStyleInvalidation(*this);
+}
+
 void Document::updateDistributionForNodeIfNeeded(Node* node)
 {
     if (node->inDocument()) {
@@ -1658,6 +1673,7 @@ void Document::inheritHtmlAndBodyElementStyles(StyleRecalcChange change)
     }
 }
 
+// FIXME: need a better name than recalcStyle. It's performing style invalidation, style recalc, and distribution.
 void Document::recalcStyle(StyleRecalcChange change)
 {
     // we should not enter style recalc while painting
@@ -1677,6 +1693,7 @@ void Document::recalcStyle(StyleRecalcChange change)
 
     updateDistributionIfNeeded();
     updateUseShadowTrees();
+    updateStyleInvalidationIfNeeded();
 
     if (m_evaluateMediaQueriesOnStyleRecalc) {
         m_evaluateMediaQueriesOnStyleRecalc = false;
@@ -1779,7 +1796,7 @@ void Document::updateStyleForNodeIfNeeded(Node* node)
     // the path from 'node' to the root needs style recalc.
 
     // Global needed.
-    bool needsRecalc = needsStyleRecalc() || childNeedsDistributionRecalc() || !m_useElementsNeedingUpdate.isEmpty();
+    bool needsRecalc = needsStyleRecalc() || childNeedsDistributionRecalc() || !m_useElementsNeedingUpdate.isEmpty() || childNeedsStyleInvalidation();
 
     // On the path.
     for (Node* ancestor = node; ancestor && !needsRecalc; ancestor = ancestor->parentOrShadowHostNode())