replace .len() == 0 with is_empty()

closes #7198

components/script/dom/bindings/str.rs

@@ -50,7 +50,7 @@ impl ByteString {
     /// [RFC 2616](http://tools.ietf.org/html/rfc2616#page-17).
     pub fn is_token(&self) -> bool {
         let ByteString(ref vec) = *self;
-        if vec.len() == 0 {
+        if vec.is_empty() {
             return false; // A token must be at least a single character
         }
         vec.iter().all(|&x| {

components/script/dom/document.rs

@@ -970,7 +970,7 @@ impl<'a> DocumentHelpers<'a> for &'a Document {
     /// https://html.spec.whatwg.org/multipage/#dom-window-cancelanimationframe
     fn cancel_animation_frame(self, ident: i32) {
         self.animation_frame_list.borrow_mut().remove(&ident);
-        if self.animation_frame_list.borrow().len() == 0 {
+        if self.animation_frame_list.borrow().is_empty() {
             let window = self.window.root();
             let window = window.r();
             let ConstellationChan(ref chan) = window.constellation_chan();

components/script/dom/htmlscriptelement.rs

@@ -231,7 +231,7 @@ impl<'a> HTMLScriptElementHelpers for &'a HTMLScriptElement {
         }
         // Step 4.
         let text = self.Text();
-        if text.len() == 0 && !element.has_attribute(&atom!("src")) {
+        if text.is_empty() && !element.has_attribute(&atom!("src")) {
             return NextParserState::Continue;
         }
         // Step 5.

components/script/dom/node.rs

@@ -2135,7 +2135,7 @@ impl<'a> NodeMethods for &'a Node {
             NodeTypeId::DocumentFragment |
             NodeTypeId::Element(..) => {
                 // Step 1-2.
-                let node = if value.len() == 0 {
+                let node = if value.is_empty() {
                     None
                 } else {
                     let document = self.owner_doc();

components/script/dom/xmlhttprequest.rs

@@ -497,7 +497,7 @@ impl<'a> XMLHttpRequestMethods for &'a XMLHttpRequest {
         // Step 7
         self.upload_complete.set(match extracted {
             None => true,
-            Some (ref v) if v.len() == 0 => true,
+            Some (ref v) if v.is_empty() => true,
             _ => false
         });