Make arguments to insertAdjacentHTML method non-optional

LayoutTests/fast/dynamic/insertAdjacentHTML.html

Index: LayoutTests/fast/dynamic/insertAdjacentHTML.html
diff --git a/LayoutTests/fast/dynamic/insertAdjacentHTML.html b/LayoutTests/fast/dynamic/insertAdjacentHTML.html
index 7013597ab21636af300a059b5308ddfe92dab86a..52b13b6faa9ec43b030e85198d16e28520f9a13c 100644
--- a/LayoutTests/fast/dynamic/insertAdjacentHTML.html
+++ b/LayoutTests/fast/dynamic/insertAdjacentHTML.html
@@ -40,6 +40,14 @@ if (window.testRunner)
       document.createElement('div').insertAdjacentHTML("afterEnd", "<span>html</span>");
    }) && passes;
 
+   passes = assertThrows(function() {
+       document.getElementById("container").insertAdjacentHTML();
+   }) && passes;
+
+   passes = assertThrows(function() {
+       document.getElementById("container").insertAdjacentHTML("beforeBegin");
+   }) && passes;
+
    if (passes) {
       document.getElementById("status").style.color = "green";
       document.getElementById("status").innerHTML = "<br><br>PASS";