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

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2011 Apple Inc.
  *               All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved.
  *               (http://www.torchmobile.com/)
@@ skipping 1912 matching lines @@
       frame->localFrameRoot()->eventHandler().scheduleCursorUpdate();
     }
   }
 
   if (diff.needsFullPaintInvalidation() && oldStyle) {
     if (resolveColor(*oldStyle, CSSPropertyBackgroundColor) !=
             resolveColor(CSSPropertyBackgroundColor) ||
         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() {
   // FIXME: We could save this call when the change only affected non-inherited
   // properties.
   for (LayoutObject* child = slowFirstChild(); child;
        child = child->nextSibling()) {
     if (!child->isAnonymous() || child->style()->styleType() != PseudoIdNone)
       continue;
 
@@ skipping 1626 matching lines @@
     const blink::LayoutObject* root = object1;
     while (root->parent())
       root = root->parent();
     root->showLayoutTreeAndMark(object1, "*", object2, "-", 0);
   } else {
     WTFLogAlways("%s", "Cannot showLayoutTree. Root is (nil)");
   }
 }
 
 #endif