Make initEvent's first argument non-optional

whatwg/dom#387

BUG=673698

Review-Url: https://codereview.chromium.org/2579993002
Cr-Commit-Position: refs/heads/master@{#458108}

third_party/WebKit/LayoutTests/external/wpt/dom/interfaces-expected.txt

@@ -1,5 +1,5 @@
 This is a testharness.js-based test.
-Found 1609 tests; 1423 PASS, 186 FAIL, 0 TIMEOUT, 0 NOTRUN.
+Found 1609 tests; 1428 PASS, 181 FAIL, 0 TIMEOUT, 0 NOTRUN.
 PASS Event interface: existence and properties of interface object 
 PASS Event interface object length 
 PASS Event interface object name 
@@ -24,7 +24,7 @@ PASS Event interface: attribute cancelable
 PASS Event interface: operation preventDefault() 
 PASS Event interface: attribute defaultPrevented 
 PASS Event interface: attribute timeStamp 
-FAIL Event interface: operation initEvent(DOMString,boolean,boolean) assert_equals: property has wrong .length expected 1 but got 0
+PASS Event interface: operation initEvent(DOMString,boolean,boolean) 
 PASS Event must be primary interface of document.createEvent("Event") 
 PASS Stringification of document.createEvent("Event") 
 PASS Event interface: document.createEvent("Event") must inherit property "type" with the proper type (0) 
@@ -44,9 +44,7 @@ PASS Event interface: document.createEvent("Event") must inherit property "defau
 PASS Event interface: document.createEvent("Event") must have own property "isTrusted" 
 PASS Event interface: document.createEvent("Event") must inherit property "timeStamp" with the proper type (15) 
 PASS Event interface: document.createEvent("Event") must inherit property "initEvent" with the proper type (16) 
-FAIL Event interface: calling initEvent(DOMString,boolean,boolean) on document.createEvent("Event") with too few arguments must throw TypeError assert_throws: Called with 0 arguments function "function () {
-            fn.apply(obj, args);
-        }" did not throw
+PASS Event interface: calling initEvent(DOMString,boolean,boolean) on document.createEvent("Event") with too few arguments must throw TypeError 
 PASS Event must be primary interface of new Event("foo") 
 PASS Stringification of new Event("foo") 
 PASS Event interface: new Event("foo") must inherit property "type" with the proper type (0) 
@@ -66,9 +64,7 @@ PASS Event interface: new Event("foo") must inherit property "defaultPrevented"
 PASS Event interface: new Event("foo") must have own property "isTrusted" 
 PASS Event interface: new Event("foo") must inherit property "timeStamp" with the proper type (15) 
 PASS Event interface: new Event("foo") must inherit property "initEvent" with the proper type (16) 
-FAIL Event interface: calling initEvent(DOMString,boolean,boolean) on new Event("foo") with too few arguments must throw TypeError assert_throws: Called with 0 arguments function "function () {
-            fn.apply(obj, args);
-        }" did not throw
+PASS Event interface: calling initEvent(DOMString,boolean,boolean) on new Event("foo") with too few arguments must throw TypeError 
 PASS CustomEvent interface: existence and properties of interface object 
 PASS CustomEvent interface object length 
 PASS CustomEvent interface object name 
@@ -98,9 +94,7 @@ PASS Event interface: new CustomEvent("foo") must inherit property "defaultPreve
 PASS Event interface: new CustomEvent("foo") must have own property "isTrusted" 
 PASS Event interface: new CustomEvent("foo") must inherit property "timeStamp" with the proper type (15) 
 PASS Event interface: new CustomEvent("foo") must inherit property "initEvent" with the proper type (16) 
-FAIL Event interface: calling initEvent(DOMString,boolean,boolean) on new CustomEvent("foo") with too few arguments must throw TypeError assert_throws: Called with 0 arguments function "function () {
-            fn.apply(obj, args);
-        }" did not throw
+PASS Event interface: calling initEvent(DOMString,boolean,boolean) on new CustomEvent("foo") with too few arguments must throw TypeError 
 PASS EventTarget interface: existence and properties of interface object 
 PASS EventTarget interface object length 
 PASS EventTarget interface object name