Convert Intos to Froms.

src/liballoc/string.rs

@@ -2009,9 +2009,9 @@ impl From<Box<str>> for String {
 }
 
 #[stable(feature = "box_from_str", since = "1.18.0")]
-impl Into<Box<str>> for String {
-    fn into(self) -> Box<str> {
-        self.into_boxed_str()
+impl From<String> for Box<str> {
+    fn from(s: String) -> Box<str> {
+        s.into_boxed_str()
     }
 }