Fix line cache when `-webkit-line-clamp` is specified

|NGBlockLayoutAlgorithm| has two branches, one when
|lines_until_clamp_| becomes |<= 0| by the layout, and another
when it is |== 0|.

To make sure we run all these logic, this patch:
* Updates |lines_until_clamp_| by the number of reused lines.
* Limits reusing only up to 1, so that conditions above go
  normal layout codepath.

Bug: 1140951
Change-Id: I15fe81b4957fe70d23bb88aae700642297bb1550
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2491561Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819867}

third_party/blink/renderer/core/layout/ng/inline/ng_fragment_items_builder.cc

@@ -199,7 +199,8 @@ NGFragmentItemsBuilder::AddPreviousItems(
     const NGFragmentItems& items,
     const PhysicalSize& container_size,
     NGBoxFragmentBuilder* container_builder,
-    const NGFragmentItem* end_item) {
+    const NGFragmentItem* end_item,
+    wtf_size_t max_lines) {
   if (end_item) {
     DCHECK(node_);
     DCHECK(container_builder);
@@ -235,6 +236,7 @@ NGFragmentItemsBuilder::AddPreviousItems(
   const NGInlineBreakToken* last_break_token = nullptr;
   const NGInlineItemsData* items_data = nullptr;
   LayoutUnit used_block_size;
+  wtf_size_t line_count = 0;
 
   for (NGInlineCursor cursor(items); cursor;) {
     DCHECK(cursor.Current().Item());
@@ -286,6 +288,8 @@ NGFragmentItemsBuilder::AddPreviousItems(
                 line_child.Size()),
             line_child);
       }
+      if (++line_count == max_lines)
+        break;
       cursor.MoveToNextSkippingChildren();
       continue;
     }
@@ -299,7 +303,10 @@ NGFragmentItemsBuilder::AddPreviousItems(
 
   if (end_item && last_break_token) {
     DCHECK(!last_break_token->IsFinished());
-    return AddPreviousItemsResult{last_break_token, used_block_size, true};
+    DCHECK_GT(line_count, 0u);
+    DCHECK(!max_lines || line_count <= max_lines);
+    return AddPreviousItemsResult{last_break_token, used_block_size, line_count,
+                                  true};
   }
   return AddPreviousItemsResult();
 }

third_party/blink/renderer/core/layout/ng/inline/ng_fragment_items_builder.h

@@ -89,6 +89,7 @@ class CORE_EXPORT NGFragmentItemsBuilder {
    public:
     const NGInlineBreakToken* inline_break_token = nullptr;
     LayoutUnit used_block_size;
+    wtf_size_t line_count = 0;
     bool succeeded = false;
   };
 
@@ -100,7 +101,8 @@ class CORE_EXPORT NGFragmentItemsBuilder {
       const NGFragmentItems& items,
       const PhysicalSize& container_size,
       NGBoxFragmentBuilder* container_builder = nullptr,
-      const NGFragmentItem* end_item = nullptr);
+      const NGFragmentItem* end_item = nullptr,
+      wtf_size_t max_lines = 0);
 
   struct ItemWithOffset {
     DISALLOW_NEW();

third_party/blink/renderer/core/layout/ng/ng_block_layout_algorithm.cc

@@ -992,15 +992,23 @@ bool NGBlockLayoutAlgorithm::TryReuseFragmentsFromCache(
   if (!end_item || end_item == &previous_items->front())
     return false;
 
+  wtf_size_t max_lines = 0;
+  if (lines_until_clamp_) {
+    // There is an additional logic for the last clamped line. Reuse only up to
+    // before that to use the same logic.
+    if (*lines_until_clamp_ <= 1)
+      return false;
+    max_lines = *lines_until_clamp_ - 1;
+  }
+
   const auto& children = container_builder_.Children();
   const wtf_size_t children_before = children.size();
   NGFragmentItemsBuilder* items_builder = container_builder_.ItemsBuilder();
   const NGConstraintSpace& space = ConstraintSpace();
-  DCHECK_EQ(items_builder->GetWritingMode(), space.GetWritingMode());
-  DCHECK_EQ(items_builder->Direction(), space.Direction());
-  const auto result = items_builder->AddPreviousItems(
-      *previous_items, previous_fragment.Size(), &container_builder_, end_item);
-
+  DCHECK_EQ(items_builder->GetWritingDirection(), space.GetWritingDirection());
+  const auto result =
+      items_builder->AddPreviousItems(*previous_items, previous_fragment.Size(),
+                                      &container_builder_, end_item, max_lines);
   if (UNLIKELY(!result.succeeded)) {
     DCHECK_EQ(children.size(), children_before);
     DCHECK(!result.used_block_size);
@@ -1008,6 +1016,13 @@ bool NGBlockLayoutAlgorithm::TryReuseFragmentsFromCache(
     return false;
   }
 
+  DCHECK_GT(result.line_count, 0u);
+  DCHECK(!max_lines || result.line_count <= max_lines);
+  if (lines_until_clamp_) {
+    DCHECK_GT(*lines_until_clamp_, static_cast<int>(result.line_count));
+    lines_until_clamp_ = *lines_until_clamp_ - result.line_count;
+  }
+
   // |AddPreviousItems| may have added more than one lines. Propagate baselines
   // from them.
   for (const auto& child : base::make_span(children).subspan(children_before)) {

third_party/blink/web_tests/external/wpt/css/css-overflow/reference/webkit-line-clamp-dynamic-001-ref.html

+<!DOCTYPE html>
+<style>
+#container {
+  display: -webkit-box;
+  -webkit-line-clamp: 2;
+  -webkit-box-orient: vertical;
+  font-size: 20px;
+  width: 10ch;
+}
+</style>
+<body>
+  <div id="container">
+    abc def ghi jkl mno pqr stu vwx yz
+    123 456 789
+  </div>
+</body>

third_party/blink/web_tests/external/wpt/css/css-overflow/webkit-line-clamp-dynamic-001.html

+<!DOCTYPE html>
+<title>CSS Overflow: appending to a box with -webkit-line-clamp</title>
+<link rel="help" href="https://drafts.csswg.org/css-overflow-3/#webkit-line-clamp">
+<link rel="match" href="reference/webkit-line-clamp-dynamic-001-ref.html">
+<link rel="author" title="Koji Ishii" href="mailto:kojii@chromium.org">
+<style>
+#container {
+  display: -webkit-box;
+  -webkit-line-clamp: 2;
+  -webkit-box-orient: vertical;
+  font-size: 20px;
+  width: 10ch;
+}
+</style>
+<body>
+  <div id="container">
+    abc def ghi jkl mno pqr stu vwx yz
+  </div>
+<script>
+testAppend();
+function testAppend() {
+  document.body.offsetTop;
+  let span = document.createElement('span');
+  span.textContent = '123 456 789';
+  container.appendChild(span);
+}
+</script>
+</body>