Added in-place mutation to DOMString.

The methods which are currently implemented are the ones on String that are currently being used:
string.push_str(...), string.clear() and string.extend(...). We may want to revisit this API.

components/script/dom/characterdata.rs

@@ -69,6 +69,7 @@ impl CharacterDataMethods for CharacterData {
 
     // https://dom.spec.whatwg.org/#dom-characterdata-appenddatadata
     fn AppendData(&self, data: DOMString) {
+        // FIXME(ajeffrey): Efficient append on DOMStrings?
         self.append_data(&*data);
     }
 
@@ -149,7 +150,8 @@ impl CharacterData {
     }
     #[inline]
     pub fn append_data(&self, data: &str) {
-        self.data.borrow_mut().0.push_str(data);
+        // FIXME(ajeffrey): Efficient append on DOMStrings?
+        self.data.borrow_mut().push_str(data);
         self.content_changed();
     }
 

components/script/dom/htmlanchorelement.rs

@@ -182,7 +182,7 @@ fn follow_hyperlink(subject: &Element, hyperlink_suffix: Option<String>) {
     // Step 6.
     // https://www.w3.org/Bugs/Public/show_bug.cgi?id=28925
     if let Some(suffix) = hyperlink_suffix {
-        href.0.push_str(&suffix);
+        href.push_str(&suffix);
     }
 
     // Step 4-5.

components/script/dom/htmlinputelement.rs

@@ -576,10 +576,11 @@ impl VirtualMethods for HTMLInputElement {
                     mutation.new_value(attr).as_ref().map(|name| name.as_atom()));
             },
             &atom!(placeholder) => {
+                // FIXME(ajeffrey): Should we do in-place mutation of the placeholder?
                 let mut placeholder = self.placeholder.borrow_mut();
-                placeholder.0.clear();
+                placeholder.clear();
                 if let AttributeMutation::Set(_) = mutation {
-                    placeholder.0.extend(
+                    placeholder.extend(
                         attr.value().chars().filter(|&c| c != '\n' && c != '\r'));
                 }
             },

components/script/textinput.rs

@@ -186,6 +186,7 @@ impl<T: ClipboardProvider> TextInput<T> {
                     vec!(insert)
                 };
 
+                // FIXME(ajeffrey): effecient append for DOMStrings
                 let mut new_line = prefix.to_owned();
                 new_line.push_str(&insert_lines[0]);
                 insert_lines[0] = DOMString::from(new_line);
@@ -194,7 +195,8 @@ impl<T: ClipboardProvider> TextInput<T> {
                 self.edit_point.index = insert_lines[last_insert_lines_index].len();
                 self.edit_point.line = begin.line + last_insert_lines_index;
 
-                insert_lines[last_insert_lines_index].0.push_str(suffix);
+                // FIXME(ajeffrey): effecient append for DOMStrings
+                insert_lines[last_insert_lines_index].push_str(suffix);
 
                 let mut new_lines = vec!();
                 new_lines.push_all(lines_prefix);

components/util/str.rs

@@ -32,6 +32,13 @@ impl DOMString {
     pub fn new() -> DOMString {
         DOMString(String::new())
     }
+    // FIXME(ajeffrey): implement more of the String methods on DOMString?
+    pub fn push_str(&mut self, string: &str) {
+        self.0.push_str(string)
+    }
+    pub fn clear(&mut self) {
+        self.0.clear()
+    }
 }
 
 impl Default for DOMString {
@@ -181,6 +188,12 @@ impl FromJSValConvertible for DOMString {
     }
 }
 
+impl Extend<char> for DOMString {
+    fn extend<I>(&mut self, iterable: I) where I: IntoIterator<Item=char> {
+        self.0.extend(iterable)
+    }
+}
+
 pub type StaticCharVec = &'static [char];
 pub type StaticStringVec = &'static [&'static str];