Add a use counter for `unicode-bidi: plaintext`

To measure the usage to help discussions.

Change-Id: Iaaada2de6899c38edd3f4be5624c832dfd119a14
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2470896
Commit-Queue: Ian Kilpatrick <ikilpatrick@chromium.org>
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#817016}

third_party/blink/public/mojom/web_feature/web_feature.mojom

@@ -3034,6 +3034,7 @@ enum WebFeature {
   kNewLayoutOverflowDifferentFlex = 3703,
   kNewLayoutOverflowDifferentAndAlreadyScrollsBlock = 3704,
   kNewLayoutOverflowDifferentAndAlreadyScrollsFlex = 3705,
+  kUnicodeBidiPlainText = 3706,
 
   // Add new features immediately above this line. Don't change assigned
   // numbers of any item, and don't reuse removed slots.

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

@@ -1085,7 +1085,7 @@ void NGInlineItemsBuilderTemplate<OffsetMappingBuilder>::EnterBlock(
         has_bidi_controls_ = true;
         // It's not easy to compute which lines will change with `unicode-bidi:
         // plaintext`. Since it is quite uncommon that just disable line cache.
-        changes_may_affect_earlier_lines_ = true;
+        has_unicode_bidi_plain_text_ = true;
         break;
     }
   } else {
@@ -1129,7 +1129,7 @@ void NGInlineItemsBuilderTemplate<OffsetMappingBuilder>::EnterInline(
                          kPopDirectionalIsolateCharacter);
         break;
       case UnicodeBidi::kPlaintext:
-        changes_may_affect_earlier_lines_ = true;
+        has_unicode_bidi_plain_text_ = true;
         EnterBidiContext(node, kFirstStrongIsolateCharacter,
                          kPopDirectionalIsolateCharacter);
         break;
@@ -1251,7 +1251,7 @@ void NGInlineItemsBuilderTemplate<
   data->has_ruby_ = has_ruby_;
   data->is_empty_inline_ = IsEmptyInline();
   data->is_block_level_ = IsBlockLevel();
-  data->changes_may_affect_earlier_lines_ = ChangesMayAffectEarlierLines();
+  data->changes_may_affect_earlier_lines_ = HasUnicodeBidiPlainText();
 }
 
 template <typename OffsetMappingBuilder>

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

@@ -62,12 +62,10 @@ class NGInlineItemsBuilderTemplate {
 
   bool IsBlockLevel() const { return is_block_level_; }
 
-  // True if changes to an item may affect different layout of earlier lines.
-  // May not be able to use line caches even when the line or earlier lines are
-  // not dirty.
-  bool ChangesMayAffectEarlierLines() const {
-    return changes_may_affect_earlier_lines_;
-  }
+  // True if there were any `unicode-bidi: plaintext`. In this case, changes to
+  // an item may affect different layout of earlier lines. May not be able to
+  // use line caches even when the line or earlier lines are not dirty.
+  bool HasUnicodeBidiPlainText() const { return has_unicode_bidi_plain_text_; }
 
   // Append a string from |LayoutText|.
   //
@@ -184,7 +182,7 @@ class NGInlineItemsBuilderTemplate {
   bool has_ruby_ = false;
   bool is_empty_inline_ = true;
   bool is_block_level_ = true;
-  bool changes_may_affect_earlier_lines_ = false;
+  bool has_unicode_bidi_plain_text_ = false;
 
   // Append a character.
   // Currently this function is for adding control characters such as

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

@@ -954,6 +954,9 @@ void NGInlineNode::CollectInlines(NGInlineNodeData* data,
   NGInlineItemsBuilder builder(block, &data->items);
   CollectInlinesInternal(&builder, previous_data);
   builder.DidFinishCollectInlines(data);
+
+  if (UNLIKELY(builder.HasUnicodeBidiPlainText()))
+    UseCounter::Count(GetDocument(), WebFeature::kUnicodeBidiPlainText);
 }
 
 void NGInlineNode::SegmentText(NGInlineNodeData* data) const {

tools/metrics/histograms/enums.xml

@@ -29918,6 +29918,7 @@ Called by update_use_counter_feature_enum.py.-->
   <int value="3703" label="NewLayoutOverflowDifferentFlex"/>
   <int value="3704" label="NewLayoutOverflowDifferentAndAlreadyScrollsBlock"/>
   <int value="3705" label="NewLayoutOverflowDifferentAndAlreadyScrollsFlex"/>
+  <int value="3706" label="UnicodeBidiPlainText"/>
 </enum>
 
 <enum name="FeaturePolicyAllowlistType">