[LayoutNG] Fix empty inlines to influence the used line height

third_party/WebKit/Source/core/layout/ng/inline/ng_inline_box_state.cc

Index: third_party/WebKit/Source/core/layout/ng/inline/ng_inline_box_state.cc
diff --git a/third_party/WebKit/Source/core/layout/ng/inline/ng_inline_box_state.cc b/third_party/WebKit/Source/core/layout/ng/inline/ng_inline_box_state.cc
index ffe3456984ef16cca82af74c8772c733dc84cf8b..084904c04f75700cd849e00925645a96a8d6dd33 100644
--- a/third_party/WebKit/Source/core/layout/ng/inline/ng_inline_box_state.cc
+++ b/third_party/WebKit/Source/core/layout/ng/inline/ng_inline_box_state.cc
@@ -11,9 +11,8 @@
 
 namespace blink {
 
-void NGInlineBoxState::ComputeTextMetrics(const NGInlineItem& item,
+void NGInlineBoxState::ComputeTextMetrics(const ComputedStyle& style,
                                           FontBaseline baseline_type) {
-  const ComputedStyle& style = *item.Style();
   text_metrics = NGLineHeightMetrics(style, baseline_type);
   text_top = -text_metrics.ascent;
   text_metrics.AddLeading(style.ComputedLineHeightAsFixed());
@@ -22,23 +21,47 @@ void NGInlineBoxState::ComputeTextMetrics(const NGInlineItem& item,
   include_used_fonts = style.LineHeight().IsNegative();
 }
 
+void NGInlineBoxState::AccumulateUsedFonts(const NGInlineItem& item,
+                                           unsigned start,
+                                           unsigned end,
+                                           FontBaseline baseline_type) {
+  HashSet<const SimpleFontData*> fallback_fonts;
+  item.GetFallbackFonts(&fallback_fonts, start, end);
+  for (const auto& fallback_font : fallback_fonts) {
+    NGLineHeightMetrics fallback_metrics(fallback_font->GetFontMetrics(),
+                                         baseline_type);
+    fallback_metrics.AddLeading(
+        fallback_font->GetFontMetrics().FixedLineSpacing());
+    metrics.Unite(fallback_metrics);
+  }
+}
+
 NGInlineBoxState* NGInlineLayoutStateStack::OnBeginPlaceItems(
-    const ComputedStyle* line_style) {
+    const ComputedStyle* line_style,
+    FontBaseline baseline_type) {
   if (stack_.IsEmpty()) {
     // For the first line, push a box state for the line itself.
     stack_.Resize(1);
     NGInlineBoxState* box = &stack_.back();
     box->fragment_start = 0;
-    box->style = line_style;
-    return box;
+  } else {
+    // For the following lines, clear states that are not shared across lines.
+    for (auto& box : stack_) {
+      box.fragment_start = 0;
+      box.metrics = NGLineHeightMetrics();
+      DCHECK(box.pending_descendants.IsEmpty());
+    }
   }
 
-  // For the following lines, clear states that are not shared across lines.
-  for (auto& box : stack_) {
-    box.fragment_start = 0;
-    box.metrics = NGLineHeightMetrics();
-    DCHECK(box.pending_descendants.IsEmpty());
-  }
+  // Initialize the box state for the line box.
+  NGInlineBoxState& line_box = LineBoxState();
+  line_box.style = line_style;
+
+  // Use a "strut" (a zero-width inline box with the element's font and
+  // line height properties) as the initial metrics for the line box.
+  // https://drafts.csswg.org/css2/visudet.html#strut
+  line_box.ComputeTextMetrics(*line_style, baseline_type);
+
   return &stack_.back();
 }
 
@@ -72,7 +95,9 @@ void NGInlineLayoutStateStack::OnEndPlaceItems(
     NGInlineBoxState* box = &(*it);
     EndBoxState(box, line_box);
   }
-  line_box->UniteMetrics(stack_.front().metrics);
+
+  DCHECK(!LineBoxState().metrics.IsEmpty());
+  line_box->SetMetrics(LineBoxState().metrics);
 }
 
 void NGInlineLayoutStateStack::EndBoxState(NGInlineBoxState* box,