std: Expose SystemTime accessors on fs::Metadata

These accessors are used to get at the last modification, last access, and
creation time of the underlying file. Currently not all platforms provide the
creation time, so that currently returns `Option`.

src/libstd/time/mod.rs

@@ -16,6 +16,7 @@ use error::Error;
 use fmt;
 use ops::{Add, Sub};
 use sys::time;
+use sys_common::FromInner;
 
 #[stable(feature = "time", since = "1.3.0")]
 pub use self::duration::Duration;
@@ -227,6 +228,12 @@ impl fmt::Display for SystemTimeError {
     }
 }
 
+impl FromInner<time::SystemTime> for SystemTime {
+    fn from_inner(time: time::SystemTime) -> SystemTime {
+        SystemTime(time)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::{Instant, SystemTime, Duration, UNIX_EPOCH};