LibWeb: Implement "Document has a style sheet that is blocking scripts"

This will be used by the HTML parser to determine whether it's okay to
start running a script.

Note that we don't actually count the script-blocking style sheets yet.
This patch only adds a the checking mechanism for the parser.

Userland/Libraries/LibWeb/DOM/Document.cpp

@@ -948,4 +948,18 @@ String Document::dump_dom_tree_as_json() const
     return builder.to_string();
 }
 
+// https://html.spec.whatwg.org/multipage/semantics.html#has-a-style-sheet-that-is-blocking-scripts
+bool Document::has_a_style_sheet_that_is_blocking_scripts() const
+{
+    // A Document has a style sheet that is blocking scripts if its script-blocking style sheet counter is greater than 0,
+    if (m_script_blocking_style_sheet_counter > 0)
+        return true;
+
+    // ...or if that Document has a non-null browsing context whose container document is non-null and has a script-blocking style sheet counter greater than 0.
+    if (!browsing_context() || !browsing_context()->container_document())
+        return false;
+
+    return browsing_context()->container_document()->m_script_blocking_style_sheet_counter > 0;
+}
+
 }

Userland/Libraries/LibWeb/DOM/Document.h

@@ -270,6 +270,8 @@ public:
 
     String dump_dom_tree_as_json() const;
 
+    bool has_a_style_sheet_that_is_blocking_scripts() const;
+
 private:
     explicit Document(const URL&);
 
@@ -347,6 +349,9 @@ private:
     bool m_should_invalidate_styles_on_attribute_changes { true };
 
     u32 m_ignore_destructive_writes_counter { 0 };
+
+    // https://html.spec.whatwg.org/multipage/semantics.html#script-blocking-style-sheet-counter
+    u32 m_script_blocking_style_sheet_counter { 0 };
 };
 
 }