Inline Iterator as IntoIterator.

Author: cjgillot

Diff for: core/src/iter/traits/collect.rs

@@ -238,6 +238,7 @@ impl<I: Iterator> IntoIterator for I {
     type Item = I::Item;
     type IntoIter = I;
 
+    #[inline]
     fn into_iter(self) -> I {
         self
     }