Correct handling of |for| and |event| attributes of script elements.

https://html.spec.whatwg.org/multipage/scripting.html#script-processing-for
> 12. If the script element has an event attribute and a for attribute, then run
> these substeps:

Our implementation was "... has a non-empty event attribute and a non-empty for
attribute, ...".  This CL corrects isEmpty() checks to isNull().
The new behavior is compatible with IE and Firefox.

BUG=520844

Review URL: https://codereview.chromium.org/1305213005

git-svn-id: svn://svn.chromium.org/blink/trunk@201627 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/LayoutTests/TestExpectations

@@ -394,9 +394,6 @@ crbug.com/508725 imported/web-platform-tests/html/semantics/forms/textfieldselec
 crbug.com/490511 imported/web-platform-tests/html/semantics/text-level-semantics/the-wbr-element/wbr-element.html [ ImageOnlyFailure ]
 crbug.com/490511 imported/web-platform-tests/html/semantics/embedded-content/media-elements/interfaces/HTMLElement/HTMLTrackElement/src.html [ Failure ]
 crbug.com/526920 imported/web-platform-tests/html/semantics/embedded-content/media-elements/location-of-the-media-resource/currentSrc.html [ Failure ]
-# script-for-event.html: We can't check in failure results because we also have
-# script-for-event.xhtml.
-crbug.com/520844 imported/web-platform-tests/html/semantics/scripting-1/the-script-element/script-for-event.html [ Failure ]
 crbug.com/525889 imported/web-platform-tests/html/webappapis/scripting/processing-model-2/compile-error-in-setInterval.html [ Failure ]
 crbug.com/525889 imported/web-platform-tests/html/webappapis/scripting/processing-model-2/compile-error-in-setTimeout.html [ Failure ]
 crbug.com/525889 imported/web-platform-tests/html/webappapis/scripting/processing-model-2/runtime-error-in-setInterval.html [ Failure ]

third_party/WebKit/Source/core/dom/ScriptLoader.cpp

@@ -482,16 +482,14 @@ bool ScriptLoader::isScriptForEventSupported() const
 {
     String eventAttribute = client()->eventAttributeValue();
     String forAttribute = client()->forAttributeValue();
-    if (!eventAttribute.isEmpty() && !forAttribute.isEmpty()) {
-        forAttribute = forAttribute.stripWhiteSpace();
-        if (!equalIgnoringCase(forAttribute, "window"))
-            return false;
+    if (eventAttribute.isNull() || forAttribute.isNull())
+        return true;
 
-        eventAttribute = eventAttribute.stripWhiteSpace();
-        if (!equalIgnoringCase(eventAttribute, "onload") && !equalIgnoringCase(eventAttribute, "onload()"))
-            return false;
-    }
-    return true;
+    forAttribute = forAttribute.stripWhiteSpace();
+    if (!equalIgnoringCase(forAttribute, "window"))
+        return false;
+    eventAttribute = eventAttribute.stripWhiteSpace();
+    return equalIgnoringCase(eventAttribute, "onload") || equalIgnoringCase(eventAttribute, "onload()");
 }
 
 String ScriptLoader::scriptContent() const