Repaint selection when element with ::selection style is recalculated.

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 68baec2858e10ef18b15fd7e1892c1b891a5824f..1a67a0a4cace26d6a83e5f1f79085bbbd1c33244 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.cpp
@@ -1712,6 +1712,8 @@ void LayoutObject::setStyle(PassRefPtr<ComputedStyle> style) {
   else if (diff.needsPaintInvalidationObject() ||
            updatedDiff.needsPaintInvalidationObject())
     setShouldDoFullPaintInvalidation();
+  else if (diff.needsPaintInvalidationSelection())
+    invalidatePaintForSelection();
 
   // Text nodes share style with their parents but the paint properties don't
   // apply to them, hence the !isText() check.
@@ -3467,6 +3469,23 @@ LayoutRect LayoutObject::debugRect() const {
   return rect;
 }
 
+void LayoutObject::invalidatePaintForSelection() {
+  LayoutBlock* block =
+      isLayoutBlock() ? toLayoutBlock(this) : containingBlock();

[mstensho (USE GERRIT), 2017/02/21 21:03:54]

Even if you also explain it in the commit comment, this deserves some
documentation right here, since it's kind of exotic.

So, LayoutBoxModelObject::setSelectionState() sets an accumulated state (start +
end = both) on itself and the containing block chain all the way to LayoutView,
and the code here is a consequence of that, right?

[rune, 2017/02/21 21:42:00]

OK.
Yes.

[rune, 2017/02/21 22:34:57]

Done.

+  if (!block)
+    return;
+  if (!block->hasSelectedChildren())
+    return;
+  for (LayoutObject* child = slowFirstChild(); child;

[mstensho (USE GERRIT), 2017/02/21 21:03:54]

Likewise, I think it's worth mentioning right here why we don't bother to go
deeper than the direct children.

[rune, 2017/02/21 21:42:00]

Acknowledged.

[rune, 2017/02/21 22:34:57]

Done.

+       child = child->nextSibling()) {
+    if (!child->canBeSelectionLeaf())
+      continue;
+    if (child->getSelectionState() == SelectionNone)
+      continue;
+    child->setShouldInvalidateSelection();
+  }
+}
+
 }  // namespace blink
 
 #ifndef NDEBUG