Make ::first-line invalidation work when added or removed.

third_party/WebKit/Source/core/layout/LayoutObject.cpp

Index: third_party/WebKit/Source/core/layout/LayoutObject.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutObject.cpp b/third_party/WebKit/Source/core/layout/LayoutObject.cpp
index eaf131347ee76602bf0b2eefd5e9eff3e529bf2f..9c81f60109f88fe1f4a4280d450dacfc9dafd753 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.cpp
@@ -1930,6 +1930,33 @@ void LayoutObject::styleDidChange(StyleDifference diff,
         oldStyle->backgroundLayers() != styleRef().backgroundLayers())
       setBackgroundChangedSinceLastPaintInvalidation();
   }
+
+  if (oldStyle && oldStyle->styleType() == PseudoIdNone)
+    applyPseudoStyleChanges(*oldStyle);
+}
+
+void LayoutObject::applyPseudoStyleChanges(const ComputedStyle& oldStyle) {
+  if (oldStyle.hasPseudoStyle(PseudoIdFirstLine) ||
+      styleRef().hasPseudoStyle(PseudoIdFirstLine))
+    applyFirstLineChanges(oldStyle);
+
+  // TODO(rune@opera.com): Move the invalidation for ::selection here.
+  // Instead of having a PaintInvalidationSelectionOnly PaintInvalidationType
+  // used for the element diff, we should use PaintInvalidationObject diff on
+  // the pseudo element style here instead.
+}
+
+void LayoutObject::applyFirstLineChanges(const ComputedStyle& oldStyle) {
+  RefPtr<ComputedStyle> oldPseudoStyle;
+  RefPtr<ComputedStyle> newPseudoStyle;
+  if (oldStyle.hasPseudoStyle(PseudoIdFirstLine))
+    oldPseudoStyle = oldStyle.getCachedPseudoStyle(PseudoIdFirstLine);
+  if (styleRef().hasPseudoStyle(PseudoIdFirstLine) && oldPseudoStyle)

[mstensho (USE GERRIT), 2017/03/07 10:04:26]

This will never be true if oldStyle.hasPseudoStyle(PseudoIdFirstLine) was false,
so I suggest moving it into the above block.

[rune, 2017/03/07 10:42:54]

Done.

+    newPseudoStyle = uncachedFirstLineStyle(mutableStyle());
+  if (oldPseudoStyle && newPseudoStyle)

[mstensho (USE GERRIT), 2017/03/07 10:04:26]

Ditto - if you just return after the firstLineStyleDidChange() call.

[rune, 2017/03/07 10:42:54]

Done.

+    firstLineStyleDidChange(*oldPseudoStyle, *newPseudoStyle);
+  else
+    setNeedsLayoutAndPrefWidthsRecalc(LayoutInvalidationReason::StyleChange);
 }
 
 void LayoutObject::propagateStyleToAnonymousChildren() {