LibWeb: Cache the first <base href> (in tree order) in Document

When parsing relative URLs, we have to check the first <base href> in
tree order (if one is available). This was getting *very* costly on
large DOMs with many relative urls.

This patch avoids all that repeated traversal by letting Document cache
the first <base href> and invalidating the cache whenever a <base>
element is added/removed/edited in the DOM.

The browser was stuck doing this for a *very* long time when loading
the ECMA-262 spec, and this removes that problem entirely.

1 files changed, 10 insertions, 0 deletions

diff --git a/Userland/Libraries/LibWeb/HTML/HTMLBaseElement.cpp b/Userland/Libraries/LibWeb/HTML/HTMLBaseElement.cpp
index 19f28a84fc..675442986f 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLBaseElement.cpp
+++ b/Userland/Libraries/LibWeb/HTML/HTMLBaseElement.cpp
@@ -21,6 +21,8 @@ void HTMLBaseElement::inserted()
 {
     HTMLElement::inserted();
 
+    document().update_base_element({});
+
     // The frozen base URL must be immediately set for an element whenever any of the following situations occur:
     // - The base element becomes the first base element in tree order with an href content attribute in its Document.
 
@@ -30,6 +32,12 @@ void HTMLBaseElement::inserted()
         set_the_frozen_base_url();
 }
 
+void HTMLBaseElement::removed_from(Node* parent)
+{
+    HTMLElement::removed_from(parent);
+    document().update_base_element({});
+}
+
 void HTMLBaseElement::parse_attribute(FlyString const& name, String const& value)
 {
     HTMLElement::parse_attribute(name, value);
@@ -39,6 +47,8 @@ void HTMLBaseElement::parse_attribute(FlyString const& name, String const& value
     if (name != AttributeNames::href)
         return;
 
+    document().update_base_element({});
+
     auto first_base_element_with_href_in_document = document().first_base_element_with_href_in_tree_order();
     if (first_base_element_with_href_in_document.ptr() == this)
         set_the_frozen_base_url();