Implement "child text content" concept; use it where appropriate.

components/script/dom/document.rs

@@ -2667,7 +2667,7 @@ impl DocumentMethods for Document {
             None => DOMString::new(),
             Some(ref title) => {
                 // Steps 3-4.
-                let value = Node::collect_text_contents(title.children());
+                let value = title.child_text_content();
                 DOMString::from(str_join(split_html_space_chars(&value), " "))
             },
         }

components/script/dom/htmlscriptelement.rs

@@ -713,7 +713,7 @@ impl HTMLScriptElementMethods for HTMLScriptElement {
 
     // https://html.spec.whatwg.org/multipage/#dom-script-text
     fn Text(&self) -> DOMString {
-        Node::collect_text_contents(self.upcast::<Node>().children())
+        self.upcast::<Node>().child_text_content()
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-script-text

components/script/dom/htmltitleelement.rs

@@ -8,11 +8,9 @@ use dom::bindings::codegen::Bindings::NodeBinding::NodeMethods;
 use dom::bindings::inheritance::Castable;
 use dom::bindings::js::Root;
 use dom::bindings::str::DOMString;
-use dom::characterdata::CharacterData;
 use dom::document::Document;
 use dom::htmlelement::HTMLElement;
 use dom::node::{ChildrenMutation, Node};
-use dom::text::Text;
 use dom::virtualmethods::VirtualMethods;
 use html5ever_atoms::LocalName;
 
@@ -41,13 +39,7 @@ impl HTMLTitleElement {
 impl HTMLTitleElementMethods for HTMLTitleElement {
     // https://html.spec.whatwg.org/multipage/#dom-title-text
     fn Text(&self) -> DOMString {
-        let mut content = String::new();
-        for child in self.upcast::<Node>().children() {
-            if let Some(text) = child.downcast::<Text>() {
-                content.push_str(&text.upcast::<CharacterData>().data());
-            }
-        }
-        DOMString::from(content)
+        self.upcast::<Node>().child_text_content()
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-title-text

components/script/dom/node.rs

@@ -1788,6 +1788,11 @@ impl Node {
         copy
     }
 
+    /// https://html.spec.whatwg.org/multipage/#child-text-content
+    pub fn child_text_content(&self) -> DOMString {
+        Node::collect_text_contents(self.children())
+    }
+
     pub fn collect_text_contents<T: Iterator<Item=Root<Node>>>(iterator: T) -> DOMString {
         let mut content = String::new();
         for node in iterator {