LibWeb: Do not return an exception from fetching CSS resources

The exception returned here is never used or logged. Let's just return
a null request, to make it clearer that these are not exceptions shown
to the user (thus not observable).

Libraries/LibWeb/CSS/Fetch.cpp

@@ -15,7 +15,7 @@
 namespace Web::CSS {
 
 // https://drafts.csswg.org/css-values-4/#fetch-a-style-resource
-static WebIDL::ExceptionOr<GC::Ref<Fetch::Infrastructure::Request>> fetch_a_style_resource_impl(StyleResourceURL const& url_value, StyleSheetOrDocument sheet_or_document, Fetch::Infrastructure::Request::Destination destination, CorsMode cors_mode)
+static GC::Ptr<Fetch::Infrastructure::Request> fetch_a_style_resource_impl(StyleResourceURL const& url_value, StyleSheetOrDocument sheet_or_document, Fetch::Infrastructure::Request::Destination destination, CorsMode cors_mode)
 {
     // AD-HOC: Not every caller has a CSSStyleSheet, so allow passing a Document in instead for URL completion.
     //         Spec issue: https://github.com/w3c/csswg-drafts/issues/12065
@@ -42,7 +42,7 @@ static WebIDL::ExceptionOr<GC::Ref<Fetch::Infrastructure::Request>> fetch_a_styl
 
     auto parsed_url = DOMURL::parse(url_string, base);
     if (!parsed_url.has_value())
-        return WebIDL::SimpleException { WebIDL::SimpleExceptionType::URIError, "Failed to parse URL"sv };
+        return {};
 
     // 4. Let req be a new request whose url is parsedUrl, whose destination is destination, mode is corsMode,
     //    origin is environmentSettings’s origin, credentials mode is "same-origin", use-url-credentials flag is set,
@@ -91,9 +91,12 @@ static WebIDL::ExceptionOr<GC::Ref<Fetch::Infrastructure::Request>> fetch_a_styl
 }
 
 // https://drafts.csswg.org/css-values-4/#fetch-a-style-resource
-WebIDL::ExceptionOr<GC::Ref<Fetch::Infrastructure::FetchController>> fetch_a_style_resource(StyleResourceURL const& url_value, StyleSheetOrDocument sheet_or_document, Fetch::Infrastructure::Request::Destination destination, CorsMode cors_mode, Fetch::Infrastructure::FetchAlgorithms::ProcessResponseConsumeBodyFunction process_response)
+GC::Ptr<Fetch::Infrastructure::FetchController> fetch_a_style_resource(StyleResourceURL const& url_value, StyleSheetOrDocument sheet_or_document, Fetch::Infrastructure::Request::Destination destination, CorsMode cors_mode, Fetch::Infrastructure::FetchAlgorithms::ProcessResponseConsumeBodyFunction process_response)
 {
-    auto request = TRY(fetch_a_style_resource_impl(url_value, sheet_or_document, destination, cors_mode));
+    auto request = fetch_a_style_resource_impl(url_value, sheet_or_document, destination, cors_mode);
+    if (!request)
+        return {};
+
     auto& environment_settings = HTML::relevant_settings_object(sheet_or_document.visit([](auto& it) -> JS::Object& { return it; }));
     auto& vm = environment_settings.vm();
 
@@ -114,10 +117,9 @@ GC::Ptr<HTML::SharedResourceRequest> fetch_an_external_image_for_a_stylesheet(St
     // NB: We can't directly call fetch_a_style_resource() because we want to make use of SharedResourceRequest to
     //     deduplicate image requests.
 
-    auto maybe_request = fetch_a_style_resource_impl(url_value, sheet_or_document, Fetch::Infrastructure::Request::Destination::Image, CorsMode::NoCors);
-    if (maybe_request.is_error())
-        return nullptr;
-    auto& request = maybe_request.value();
+    auto request = fetch_a_style_resource_impl(url_value, sheet_or_document, Fetch::Infrastructure::Request::Destination::Image, CorsMode::NoCors);
+    if (!request)
+        return {};
 
     auto document = sheet_or_document.visit(
         [&](GC::Ref<CSSStyleSheet> const& sheet) -> GC::Ref<DOM::Document> { return *sheet->owning_document(); },

Libraries/LibWeb/CSS/Fetch.h

@@ -25,7 +25,7 @@ using StyleResourceURL = Variant<::URL::URL, CSS::URL>;
 using StyleSheetOrDocument = Variant<GC::Ref<CSSStyleSheet>, GC::Ref<DOM::Document>>;
 
 // https://drafts.csswg.org/css-values-4/#fetch-a-style-resource
-WebIDL::ExceptionOr<GC::Ref<Fetch::Infrastructure::FetchController>> fetch_a_style_resource(StyleResourceURL const& url, StyleSheetOrDocument, Fetch::Infrastructure::Request::Destination, CorsMode, Fetch::Infrastructure::FetchAlgorithms::ProcessResponseConsumeBodyFunction process_response);
+GC::Ptr<Fetch::Infrastructure::FetchController> fetch_a_style_resource(StyleResourceURL const& url, StyleSheetOrDocument, Fetch::Infrastructure::Request::Destination, CorsMode, Fetch::Infrastructure::FetchAlgorithms::ProcessResponseConsumeBodyFunction process_response);
 
 // https://drafts.csswg.org/css-images-4/#fetch-an-external-image-for-a-stylesheet
 GC::Ptr<HTML::SharedResourceRequest> fetch_an_external_image_for_a_stylesheet(StyleResourceURL const&, StyleSheetOrDocument);

Libraries/LibWeb/CSS/StyleComputer.cpp

@@ -265,7 +265,7 @@ void FontLoader::start_loading_next_url()
     // CSS style sheet, destination "font", CORS mode "cors", and processResponse being the following steps given
     // response res and null, failure or a byte stream stream:
     auto style_sheet_or_document = m_parent_style_sheet ? StyleSheetOrDocument { *m_parent_style_sheet } : StyleSheetOrDocument { m_style_computer->document() };
-    auto maybe_fetch_controller = fetch_a_style_resource(m_urls.take_first(), style_sheet_or_document, Fetch::Infrastructure::Request::Destination::Font, CorsMode::Cors,
+    m_fetch_controller = fetch_a_style_resource(m_urls.take_first(), style_sheet_or_document, Fetch::Infrastructure::Request::Destination::Font, CorsMode::Cors,
         [loader = this](auto response, auto stream) {
             // 1. If stream is null, return.
             // 2. Load a font from stream according to its type.
@@ -290,11 +290,8 @@ void FontLoader::start_loading_next_url()
             }
         });
 
-    if (maybe_fetch_controller.is_error()) {
+    if (!m_fetch_controller)
         font_did_load_or_fail(nullptr);
-    } else {
-        m_fetch_controller = maybe_fetch_controller.release_value();
-    }
 }
 
 void FontLoader::font_did_load_or_fail(RefPtr<Gfx::Typeface const> typeface)