[LayoutNG] Compute baseline from fragment tree

third_party/WebKit/Source/core/layout/ng/ng_box_fragment.cc

Index: third_party/WebKit/Source/core/layout/ng/ng_box_fragment.cc
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_box_fragment.cc b/third_party/WebKit/Source/core/layout/ng/ng_box_fragment.cc
index 99db6d83e1faeb286bd49a50ad8494be71a007c2..175c163491abe441ed392f7740a8f0d47e36e21f 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_box_fragment.cc
+++ b/third_party/WebKit/Source/core/layout/ng/ng_box_fragment.cc
@@ -4,7 +4,9 @@
 
 #include "core/layout/ng/ng_box_fragment.h"
 
+#include "core/layout/LayoutBox.h"
 #include "core/layout/ng/geometry/ng_logical_size.h"
+#include "core/layout/ng/inline/ng_line_height_metrics.h"
 #include "core/layout/ng/ng_macros.h"
 #include "core/layout/ng/ng_physical_box_fragment.h"
 
@@ -15,4 +17,40 @@ NGLogicalSize NGBoxFragment::OverflowSize() const {
   return physical_fragment->OverflowSize().ConvertToLogical(WritingMode());
 }
 
+NGLineHeightMetrics NGBoxFragment::BaselineMetrics(
+    const NGBaselineRequest& request) const {
+  LayoutBox* layout_box = ToLayoutBox(physical_fragment_->GetLayoutObject());
+
+  // Find the baseline from the computed results.
+  const NGPhysicalBoxFragment* physical_fragment =
+      ToNGPhysicalBoxFragment(physical_fragment_);
+  if (const NGBaseline* baseline = physical_fragment->Baseline(request)) {
+    LayoutUnit ascent = baseline->offset;
+    LayoutUnit descent = BlockSize() - ascent;
+
+    // For replaced elements, inline-block elements, and inline-table
+    // elements, the height is the height of their margin box.
+    // https://drafts.csswg.org/css2/visudet.html#line-height
+    if (layout_box->IsAtomicInlineLevel()) {
+      ascent += layout_box->MarginOver();
+      descent += layout_box->MarginUnder();
+    }
+
+    return NGLineHeightMetrics(ascent, descent);
+  }
+
+  // The baseline type was not found. This is either this box should synthesize
+  // box-baseline without propagating from children, or caller forgot to add
+  // baseline requests to constraint space when it called Layout().
+  LayoutUnit block_size = BlockSize();
+
+  // If atomic inline, use the margin box. See above.
+  if (layout_box->IsAtomicInlineLevel())
+    block_size += layout_box->MarginLogicalHeight();
+
+  if (request.baseline_type == kAlphabeticBaseline)
+    return NGLineHeightMetrics(block_size, LayoutUnit());
+  return NGLineHeightMetrics(block_size - block_size / 2, block_size / 2);
+}
+
 }  // namespace blink