[css-pseudo] Cleanup list markers exclusions from anonymous boxes

Some functions check whether a LayoutObject is anonymous, and then they
exclude it if it's a list marker. However, since r745012, list markers
can never be anonymous, they are always generated by a ::marker pseudo-
element. Therefore, the condition is useless and can be removed.

BUG=457718

Change-Id: I5e2636f68fab483838e8a5227ccace34b6de22cc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2250102Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Oriol Brufau <obrufau@igalia.com>
Cr-Commit-Position: refs/heads/master@{#779781}

third_party/blink/renderer/core/layout/layout_block_flow.cc

@@ -3101,8 +3101,7 @@ void LayoutBlockFlow::RemoveChild(LayoutObject* old_child) {
 
     // If we are an empty anonymous block in the continuation chain,
     // we need to remove ourself and fix the continuation chain.
-    if (!BeingDestroyed() && IsAnonymousBlockContinuation() &&
-        !old_child->IsListMarker()) {
+    if (!BeingDestroyed() && IsAnonymousBlockContinuation()) {
       LayoutObject* containing_block_ignoring_anonymous = ContainingBlock();
       while (containing_block_ignoring_anonymous &&
              containing_block_ignoring_anonymous->IsAnonymous())

third_party/blink/renderer/core/layout/layout_object.h

@@ -960,8 +960,7 @@ class CORE_EXPORT LayoutObject : public ImageResourceObserver,
            (StyleRef().Display() == EDisplay::kBlock ||
             StyleRef().Display() == EDisplay::kWebkitBox) &&
            StyleRef().StyleType() == kPseudoIdNone && IsLayoutBlock() &&
-           !IsListMarker() && !IsLayoutFlowThread() &&
-           !IsLayoutMultiColumnSet();
+           !IsLayoutFlowThread() && !IsLayoutMultiColumnSet();
   }
   // If node has been split into continuations, it returns the first layout
   // object generated for the node.