Aligned srcset mixedContent blocking to the spec

Source/core/loader/ImageLoader.cpp

Index: Source/core/loader/ImageLoader.cpp
diff --git a/Source/core/loader/ImageLoader.cpp b/Source/core/loader/ImageLoader.cpp
index 37af0a02ced31eded5a0cd5460e74bb77025e99b..343f289b415bc433c622204ed3a8daa5505dd4a9 100644
--- a/Source/core/loader/ImageLoader.cpp
+++ b/Source/core/loader/ImageLoader.cpp
@@ -242,7 +242,7 @@ void ImageLoader::doUpdateFromElement(BypassMainWorldBehavior bypassBehavior, Up
         // Unlike raw <img>, we block mixed content inside of <picture> or <img srcset>.
         ResourceLoaderOptions resourceLoaderOptions = ResourceFetcher::defaultResourceOptions();
         ResourceRequest resourceRequest(url);
-        if (isHTMLPictureElement(element()->parentNode()) || !element()->fastGetAttribute(HTMLNames::srcsetAttr).isEmpty()) {
+        if (isHTMLPictureElement(element()->parentNode()) || !element()->fastGetAttribute(HTMLNames::srcsetAttr).isNull()) {
             resourceLoaderOptions.mixedContentBlockingTreatment = TreatAsActiveContent;
             resourceRequest.setRequestContext(WebURLRequest::RequestContextImageSet);
         }