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

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

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/layout/ng/inline/ng_inline_box_state.h"
 
 #include "core/layout/ng/inline/ng_inline_node.h"
 #include "core/layout/ng/inline/ng_line_box_fragment_builder.h"
 #include "core/layout/ng/inline/ng_text_fragment_builder.h"
 #include "core/style/ComputedStyle.h"
 
 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());
   metrics.Unite(text_metrics);
 
   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();
 }
 
 NGInlineBoxState* NGInlineLayoutStateStack::OnOpenTag(
     const NGInlineItem& item,
     NGLineBoxFragmentBuilder* line_box,
     NGTextFragmentBuilder* text_builder) {
   stack_.Resize(stack_.size() + 1);
   NGInlineBoxState* box = &stack_.back();
   box->fragment_start = line_box->Children().size();
@@ skipping 13 matching lines @@
   stack_.pop_back();
   return &stack_.back();
 }
 
 void NGInlineLayoutStateStack::OnEndPlaceItems(
     NGLineBoxFragmentBuilder* line_box) {
   for (auto it = stack_.rbegin(); it != stack_.rend(); ++it) {
     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,
                                            NGLineBoxFragmentBuilder* line_box) {
   ApplyBaselineShift(box, line_box);
 
   // Unite the metrics to the parent box.
   if (box != stack_.begin()) {
     box[-1].metrics.Unite(box->metrics);
   }
@@ skipping 78 matching lines @@
       box[-1].pending_descendants.push_back(NGPendingPositions{
           box->fragment_start, fragment_end, box->metrics, vertical_align});
       return;
   }
   box->metrics.Move(baseline_shift);
   line_box->MoveChildrenInBlockDirection(baseline_shift, box->fragment_start,
                                          fragment_end);
 }
 
 }  // namespace blink