The following two unit tests differ only in the enabled status of LayoutNG, but the second one fails by reporting zero margin instead:

TEST_F(NGInlineLayoutTest, PWithoutLayoutNG) {
  RuntimeEnabledFeatures::SetLayoutNGEnabled(false);

  SimRequest main_resource("https://example.com/", "text/html");
  LoadURL("https://example.com/");
  main_resource.Complete(
      "<p id=\"target\">foo bar baz</p>");

  Compositor().BeginFrame();
  ASSERT_FALSE(Compositor().NeedsBeginFrame());

  Element* target = GetDocument().getElementById("target");
  LayoutBox* box = ToLayoutBox(target->GetLayoutObject());

  EXPECT_EQ(1.0, box->MarginTop().ToDouble());
  EXPECT_EQ(1.0, box->MarginBottom().ToDouble());
  EXPECT_EQ(0.0, box->MarginLeft().ToDouble());
  EXPECT_EQ(0.0, box->MarginRight().ToDouble());
}

TEST_F(NGInlineLayoutTest, PWithLayoutNG) {
  RuntimeEnabledFeatures::SetLayoutNGEnabled(true);

  SimRequest main_resource("https://example.com/", "text/html");
  LoadURL("https://example.com/");
  main_resource.Complete(
      "<p id=\"target\">foo bar baz</p>");

  Compositor().BeginFrame();
  ASSERT_FALSE(Compositor().NeedsBeginFrame());

  Element* target = GetDocument().getElementById("target");
  LayoutBox* box = ToLayoutBox(target->GetLayoutObject());

  EXPECT_EQ(1.0, box->MarginTop().ToDouble());
  EXPECT_EQ(1.0, box->MarginBottom().ToDouble());
  EXPECT_EQ(0.0, box->MarginLeft().ToDouble());
  EXPECT_EQ(0.0, box->MarginRight().ToDouble());
}

A deeper investigation shows that, the margin of <p> is never set in the second test.