[css-grid] Add test for Grid Items Sizing

Now that issue w3c/csswg-drafts#523 has been resolved,
I'm adding a new test to verify the default alignment ("normal")
for replaced and non-replaced elements.
diff --git a/css-grid-1/grid-items/grid-items-sizing-alignment-001-ref.html b/css-grid-1/grid-items/grid-items-sizing-alignment-001-ref.html
new file mode 100644
index 0000000..859483c
--- /dev/null
+++ b/css-grid-1/grid-items/grid-items-sizing-alignment-001-ref.html
@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>CSS Reftest Reference: Grid Item Sizing</title>
+<link rel="author" title="Manuel Rego Casasnovas" href="mailto:rego@igalia.com">
+
+<p>Test passes if it has the same output than the reference.</p>
+
+<div id="grid">
+  <button style="width: 200px; height: 200px;">Stretched button (200x200)</button><button style="width: 200px; height: 200px;">Stretched button (200x200)</button><button style="vertical-align: top;">Regular button</button>
+  <br>
+  <img style="vertical-align: top; margin-right: 150px;" src="support/50x50-green.png" alt="Image download support must be enabled" /><img src="support/200x200-green.png" alt="Image download support must be enabled" /><img style="vertical-align: top;" src="support/50x50-green.png" alt="Image download support must be enabled" />
+</div>
+
diff --git a/css-grid-1/grid-items/grid-items-sizing-alignment-001.html b/css-grid-1/grid-items/grid-items-sizing-alignment-001.html
new file mode 100644
index 0000000..de9ed04
--- /dev/null
+++ b/css-grid-1/grid-items/grid-items-sizing-alignment-001.html
@@ -0,0 +1,27 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>CSS Grid Layout Test: Grid Item Sizing</title>
+<link rel="author" title="Manuel Rego Casasnovas" href="mailto:rego@igalia.com">
+<link rel="help" href="https://www.w3.org/TR/css-grid-1/#grid-item-sizing">
+<link rel="match" href="../reference/grid-items-sizing-alignment-001-ref.html" />
+<meta name="assert" content="Checks how alignment properties affect the size of the non-replaced vs replaced grid items.">
+<style>
+  #grid {
+    display: grid;
+    grid-auto-rows: 200px;
+    grid-template-columns: repeat(3, 200px);
+  }
+</style>
+
+<p>Test passes if it has the same output than the reference.</p>
+
+<div id="grid">
+  <button>Stretched button (200x200)</button>
+  <button style="align-self: stretch; justify-self: stretch;">Stretched button (200x200)</button>
+  <button style="align-self: start; justify-self: start;">Regular button</button>
+  <img src="support/50x50-green.png" alt="Image download support must be enabled" />
+  <img src="support/50x50-green.png" alt="Image download support must be enabled"
+    style="align-self: stretch; justify-self: stretch;" />
+  <img src="support/50x50-green.png" alt="Image download support must be enabled"
+    style="align-self: start; justify-self: start;" />
+</div>
diff --git a/css-grid-1/grid-items/support/50x50-green.png b/css-grid-1/grid-items/support/50x50-green.png
new file mode 100644
index 0000000..f709bf0
--- /dev/null
+++ b/css-grid-1/grid-items/support/50x50-green.png
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