LibWeb: Paint 1x1 backgrounds as color fill instead of tiling bitmap

This yields a huge speedup on pages that use this weird but
not-entirely-uncommon technique.

Userland/Libraries/LibWeb/CSS/StyleValues/ImageStyleValue.cpp

@@ -146,4 +146,13 @@ JS::GCPtr<HTML::DecodedImageData> ImageStyleValue::image_data() const
     return m_image_request->image_data();
 }
 
+Optional<Gfx::Color> ImageStyleValue::color_if_single_pixel_bitmap() const
+{
+    if (auto const* b = bitmap(m_current_frame_index)) {
+        if (b->width() == 1 && b->height() == 1)
+            return b->bitmap().get_pixel(0, 0);
+    }
+    return {};
+}
+
 }