[CSS Grid Layout] Implement 'justify-items' parsing

LayoutTests/fast/alignment/resources/alignment-parsing-utils.js

Index: LayoutTests/fast/alignment/resources/alignment-parsing-utils.js
diff --git a/LayoutTests/fast/alignment/resources/alignment-parsing-utils.js b/LayoutTests/fast/alignment/resources/alignment-parsing-utils.js
new file mode 100644
index 0000000000000000000000000000000000000000..54add53c84d1a74350f7c0558afeb800591c4b28
--- /dev/null
+++ b/LayoutTests/fast/alignment/resources/alignment-parsing-utils.js
@@ -0,0 +1,27 @@
+function checkValues(element, property, propertyID, value, computedValue)
+{
+    window.element = element;
+    var elementID = element.id || "element";
+    shouldBeEqualToString("element.style." + property, value);
+    shouldBeEqualToString("window.getComputedStyle(" + elementID + ", '').getPropertyValue('" + propertyID + "')", computedValue);
+}
+
+function checkBadValues(element, property, propertyID, value)
+{
+  element.style.justifyItems = value;
+  checkValues(element, property, propertyID, "", "start");
+}
+
+function checkInitialValues(element, property, propertyID, display)
+{
+  var initial = "start";
+  if (display == "grid" || display == "flex") {
+    element.style.display = display;
+    initial = "stretch";
+  }
+
+  element.style.justifyItems = "center";
+  checkValues(element, property, propertyID, "center", "center");
+  element.style.justifyItems = "initial";
+  checkValues(element, property, propertyID, "initial", initial);
+}