[CSS Grid Layout] Disallow using <ident> and function names as <custom-ident>

LayoutTests/fast/css-grid-layout/resources/grid-definitions-parsing-utils.js

 function testGridDefinitionsValues(element, columnValue, rowValue, computedColumnValue, computedRowValue)
 {
     window.element = element;
     var elementID = element.id || "element";
     shouldBeEqualToString("window.getComputedStyle(" + elementID + ", '').getPropertyValue('grid-template-columns')", computedColumnValue || columnValue);
     shouldBeEqualToString("window.getComputedStyle(" + elementID + ", '').getPropertyValue('grid-template-rows')", computedRowValue || rowValue);
 }
 
 function testGridDefinitionsSetJSValues(columnValue, rowValue, computedColumnValue, computedRowValue, jsColumnValue, jsRowValue)
 {
@@ skipping 17 matching lines @@
     element.style.font = "10px Ahem"; // Used to resolve em font consistently.
     element.style.gridTemplateColumns = columnValue;
     element.style.gridTemplateRows = rowValue;
     shouldBeEqualToString("getComputedStyle(element, '').getPropertyValue('grid-template-columns')", computedColumnValue || columnValue);
     shouldBeEqualToString("element.style.gridTemplateColumns", jsColumnValue || columnValue);
     shouldBeEqualToString("getComputedStyle(element, '').getPropertyValue('grid-template-rows')", computedRowValue || rowValue);
     shouldBeEqualToString("element.style.gridTemplateRows", jsRowValue || rowValue);
     document.body.removeChild(element);
 }
 
+function checkGridDefinitionsSetBadJSValues(useGrid, columnValue, rowValue)
+{
+    window.element = document.createElement("div");
+    document.body.appendChild(element);
+    if (useGrid)
+        element.style.display = "grid";
+    element.style.gridTemplateColumns = columnValue;
+    element.style.gridTemplateRows = rowValue;
+    // We can't use testSetJSValues as element.style.gridTemplateRows returns "".
+    testGridDefinitionsValues(element, "none", "none");
+    document.body.removeChild(element);
+}
+
 function testGridDefinitionsSetBadJSValues(columnValue, rowValue)
 {
-    window.element = document.createElement("div");
-    document.body.appendChild(element);
-    element.style.gridTemplateColumns = columnValue;
-    element.style.gridTemplateRows = rowValue;
-    // We can't use testSetJSValues as element.style.gridTemplateRows returns "".
-    testGridDefinitionsValues(element, "none", "none");
-    document.body.removeChild(element);
-}
+    checkGridDefinitionsSetBadJSValues(true, columnValue, rowValue);
+}
+
+function testNonGridDefinitionsSetBadJSValues(columnValue, rowValue)
+{
+    checkGridDefinitionsSetBadJSValues(false, columnValue, rowValue);
+}