Remove unused imports; handle IO failure in append_serialization.

components/style/properties/properties.mako.rs

@@ -468,7 +468,7 @@ fn append_serialization<'a, W, I>(dest: &mut W,
         return append_declaration_value(dest, appendable_value, is_important);
     }
 
-    write!(dest, "{}:", property_name);
+    try!(write!(dest, "{}:", property_name));
 
     // for normal parsed values, add a space between key: and value
     match &appendable_value {

components/style/traversal.rs

@@ -6,15 +6,14 @@
 
 use animation;
 use context::{LocalStyleContext, SharedStyleContext, StyleContext};
-use dom::{OpaqueNode, TElement, TNode, TRestyleDamage, UnsafeNode};
+use dom::{OpaqueNode, TNode, TRestyleDamage, UnsafeNode};
 use matching::{ApplicableDeclarations, ElementMatchMethods, MatchMethods, StyleSharingResult};
 use selectors::bloom::BloomFilter;
 use selectors::matching::StyleRelations;
 use std::cell::RefCell;
 use std::sync::atomic::{AtomicUsize, ATOMIC_USIZE_INIT, Ordering};
 use tid::tid;
 use util::opts;
-use values::HasViewportPercentage;
 
 /// Every time we do another layout, the old bloom filters are invalid. This is
 /// detected by ticking a generation number every layout.