Skip dirtying lines when attaching children prior to attaching oneself

third_party/WebKit/Source/core/layout/line/LineBoxList.cpp

Index: third_party/WebKit/Source/core/layout/line/LineBoxList.cpp
diff --git a/third_party/WebKit/Source/core/layout/line/LineBoxList.cpp b/third_party/WebKit/Source/core/layout/line/LineBoxList.cpp
index 045661e60448b806b255d3d0a5f49ea37004351b..1a4dab9de6fc17d0c31e33d7298672a400a88f44 100644
--- a/third_party/WebKit/Source/core/layout/line/LineBoxList.cpp
+++ b/third_party/WebKit/Source/core/layout/line/LineBoxList.cpp
@@ -234,6 +234,12 @@ void LineBoxList::dirtyLinesFromChangedChild(LineLayoutItem container, LineLayou
         return;
 
     LineLayoutInline inlineContainer = container.isLayoutInline() ? LineLayoutInline(container) : LineLayoutInline();
+
+    // If we are attaching children dirtying lines is unnecessary as we will do a full layout
+    // of the inline's contents anyway.
+    if (inlineContainer && inlineContainer.node() && inlineContainer.node()->needsAttach())
+        return;
+
     InlineBox* firstBox = inlineContainer ? inlineContainer.firstLineBoxIncludingCulling() : firstLineBox();
 
     // If we have no first line box, then just bail early.