Update PseudoElements during recalcStyle.

third_party/WebKit/Source/core/style/ComputedStyle.cpp

Index: third_party/WebKit/Source/core/style/ComputedStyle.cpp
diff --git a/third_party/WebKit/Source/core/style/ComputedStyle.cpp b/third_party/WebKit/Source/core/style/ComputedStyle.cpp
index a81a1ae815f051b09bf12b604df7baa9aadce200..e15af85a1583bea07cc7de10175cd1b967ce215f 100644
--- a/third_party/WebKit/Source/core/style/ComputedStyle.cpp
+++ b/third_party/WebKit/Source/core/style/ComputedStyle.cpp
@@ -168,10 +168,14 @@ ALWAYS_INLINE ComputedStyle::ComputedStyle(const ComputedStyle& o)
 
 static StyleRecalcChange diffPseudoStyles(const ComputedStyle& oldStyle, const ComputedStyle& newStyle)
 {
-    // If the pseudoStyles have changed, we want any StyleRecalcChange that is not NoChange
-    // because setStyle will do the right thing with anything else.
-    if (!oldStyle.hasAnyPublicPseudoStyles())

[skobes, 2016/09/24 00:11:39]

We should avoid looping in the common case that neither oldStyle nor newStyle
has pseudo styles.  Can we just update the condition here to be:

if (!oldStyle.hasAnyPublicPseudoStyles() &&
!newStyle.hasAnyPublicPseudoStyles())

-        return NoChange;
+    if (!oldStyle.hasAnyPublicPseudoStyles()) {
+        // If newStyle has PseudoStyle UpdatePseudoElements will ensure layoutObject to setStyle.
+        for (PseudoId pseudoId = FirstPublicPseudoId; pseudoId < FirstInternalPseudoId; pseudoId = static_cast<PseudoId>(pseudoId + 1)) {

[skobes, 2016/09/24 00:11:39]

Instead of adding another loop let's update the main loop below to only skip if
neither oldStyle nor newStyle has the pseudo style for that id.

+            if (oldStyle.hasPseudoStyle(pseudoId) != newStyle.hasPseudoStyle(pseudoId))
+                return UpdatePseudoElements;
+        }
+    }
+
     for (PseudoId pseudoId = FirstPublicPseudoId; pseudoId < FirstInternalPseudoId; pseudoId = static_cast<PseudoId>(pseudoId + 1)) {
         if (!oldStyle.hasPseudoStyle(pseudoId))
             continue;