LibWeb: Bring up basic external script execution in the new parser

This only works in some narrow cases, but should be enough for our own
welcome.html at least. :^)

Libraries/LibWeb/Parser/HTMLDocumentParser.cpp

@@ -704,8 +704,48 @@ void HTMLDocumentParser::handle_text(HTMLToken& token)
         if (script_nesting_level() == 0)
             m_parser_pause_flag = false;
         // FIXME: Handle tokenizer insertion point stuff here too.
+
+        while (document().pending_parsing_blocking_script()) {
+            if (script_nesting_level() != 0) {
+                m_parser_pause_flag = true;
+                // FIXME: Abort the processing of any nested invocations of the tokenizer,
+                //        yielding control back to the caller. (Tokenization will resume when
+                //        the caller returns to the "outer" tree construction stage.)
+                TODO();
+            } else {
+                auto the_script = document().take_pending_parsing_blocking_script({});
+                m_tokenizer.set_blocked(true);
+
+                // FIXME: If the parser's Document has a style sheet that is blocking scripts
+                //        or the script's "ready to be parser-executed" flag is not set:
+                //        spin the event loop until the parser's Document has no style sheet
+                //        that is blocking scripts and the script's "ready to be parser-executed"
+                //        flag is set.
+
+                ASSERT(the_script->is_ready_to_be_parser_executed());
+
+                if (m_aborted)
+                    return;
+
+                m_tokenizer.set_blocked(false);
+
+                // FIXME: Handle tokenizer insertion point stuff here too.
+
+                ASSERT(script_nesting_level() == 0);
+                increment_script_nesting_level();
+
+                the_script->execute_script();
+
+                decrement_script_nesting_level();
+                ASSERT(script_nesting_level() == 0);
+                m_parser_pause_flag = false;
+
+                // FIXME: Handle tokenizer insertion point stuff here too.
+            }
+        }
         return;
     }
+
     if (token.is_end_tag()) {
         m_stack_of_open_elements.pop();
         m_insertion_mode = m_original_insertion_mode;

Libraries/LibWeb/Parser/HTMLDocumentParser.h

@@ -121,7 +121,7 @@ private:
     bool m_parsing_fragment { false };
     bool m_scripting_enabled { true };
     bool m_invoked_via_document_write { false };
-
+    bool m_aborted { false };
     bool m_parser_pause_flag { false };
     size_t m_script_nesting_level { 0 };
 

Libraries/LibWeb/Parser/HTMLTokenizer.h

@@ -130,6 +130,9 @@ public:
 
     void switch_to(Badge<HTMLDocumentParser>, State new_state);
 
+    void set_blocked(bool b) { m_blocked = b; }
+    bool is_blocked() const { return m_blocked; }
+
 private:
     Optional<u32> next_codepoint();
     Optional<u32> peek_codepoint(size_t offset) const;
@@ -172,5 +175,8 @@ private:
     Queue<HTMLToken> m_queued_tokens;
 
     u32 m_character_reference_code { 0 };
+
+    bool m_blocked { false };
 };
+
 }