Run rustfmt on selectors, servo_arc, and style.

This was generated with:

./mach cargo fmt --package selectors &&
./mach cargo fmt --package servo_arc &&
./mach cargo fmt --package style

Using rustfmt 0.4.1-nightly (a4462d1 2018-03-26)

components/style/gecko/traversal.rs

@@ -5,9 +5,9 @@
 //! Gecko-specific bits for the styling DOM traversal.
 
 use context::{SharedStyleContext, StyleContext};
-use dom::{TNode, TElement};
+use dom::{TElement, TNode};
 use gecko::wrapper::{GeckoElement, GeckoNode};
-use traversal::{DomTraversal, PerLevelTraversalData, recalc_style_at};
+use traversal::{recalc_style_at, DomTraversal, PerLevelTraversalData};
 
 /// This is the simple struct that Gecko uses to encapsulate a DOM traversal for
 /// styling.
@@ -18,19 +18,19 @@ pub struct RecalcStyleOnly<'a> {
 impl<'a> RecalcStyleOnly<'a> {
     /// Create a `RecalcStyleOnly` traversal from a `SharedStyleContext`.
     pub fn new(shared: SharedStyleContext<'a>) -> Self {
-        RecalcStyleOnly {
-            shared: shared,
-        }
+        RecalcStyleOnly { shared: shared }
     }
 }
 
 impl<'recalc, 'le> DomTraversal<GeckoElement<'le>> for RecalcStyleOnly<'recalc> {
-    fn process_preorder<F>(&self,
-                           traversal_data: &PerLevelTraversalData,
-                           context: &mut StyleContext<GeckoElement<'le>>,
-                           node: GeckoNode<'le>,
-                           note_child: F)
-        where F: FnMut(GeckoNode<'le>),
+    fn process_preorder<F>(
+        &self,
+        traversal_data: &PerLevelTraversalData,
+        context: &mut StyleContext<GeckoElement<'le>>,
+        node: GeckoNode<'le>,
+        note_child: F,
+    ) where
+        F: FnMut(GeckoNode<'le>),
     {
         if let Some(el) = node.as_element() {
             let mut data = unsafe { el.ensure_data() };
@@ -43,7 +43,9 @@ impl<'recalc, 'le> DomTraversal<GeckoElement<'le>> for RecalcStyleOnly<'recalc>
     }
 
     /// We don't use the post-order traversal for anything.
-    fn needs_postorder_traversal() -> bool { false }
+    fn needs_postorder_traversal() -> bool {
+        false
+    }
 
     fn shared_context(&self) -> &SharedStyleContext {
         &self.shared