Limit traversal statistics dumps to subtrees of 50 or more elements.

On Gecko, we get tons of console spam from 1-element traversals if we
don't do this.

components/style/context.rs

@@ -223,6 +223,12 @@ impl TraversalStatistics {
         self.is_parallel = Some(traversal.is_parallel());
         self.traversal_time_ms = (time::precise_time_s() - start) * 1000.0;
     }
+
+    /// Returns whether this traversal is 'large' in order to avoid console spam
+    /// from lots of tiny traversals.
+    pub fn is_large_traversal(&self) -> bool {
+        self.elements_traversed >= 50
+    }
 }
 
 #[cfg(feature = "gecko")]

components/style/parallel.rs

@@ -86,7 +86,9 @@ pub fn traverse_dom<E, D>(traversal: &D,
             }
         });
         aggregate.finish(traversal, start_time.unwrap());
-        println!("{}", aggregate);
+        if aggregate.is_large_traversal() {
+            println!("{}", aggregate);
+        }
     }
 }
 

components/style/sequential.rs

@@ -64,6 +64,8 @@ pub fn traverse_dom<E, D>(traversal: &D,
     if dump_stats {
         let tlsc = tlc.borrow_mut();
         tlsc.statistics.finish(traversal, start_time.unwrap());
-        println!("{}", tlsc.statistics);
+        if tlsc.statistics.is_large_traversal() {
+            println!("{}", tlsc.statistics);
+        }
     }
 }