mutex: add `OwnedMutexGuard` for `Arc<Mutex<T>>`s (#2455)

This PR adds a new `OwnedMutexGuard` type and `lock_owned` and
`try_lock_owned` methods for `Arc<Mutex<T>>`.  This is pretty much the
same as the similar APIs added in #2421. 

I've also corrected some existing documentation that incorrectly
implied that the existing `lock` method cloned an internal `Arc` — I
think this may be a holdover from `tokio` 0.1's `Lock` type?

Signed-off-by: Eliza Weisman <eliza@buoyant.io>

1 files changed, 1 insertions, 1 deletions

diff --git a/tokio/src/sync/mod.rs b/tokio/src/sync/mod.rs
index 263ec62c..359b14f5 100644
--- a/tokio/src/sync/mod.rs
+++ b/tokio/src/sync/mod.rs
@@ -428,7 +428,7 @@ cfg_sync! {
     pub mod mpsc;
 
     mod mutex;
-    pub use mutex::{Mutex, MutexGuard, TryLockError};
+    pub use mutex::{Mutex, MutexGuard, TryLockError, OwnedMutexGuard};
 
     mod notify;
     pub use notify::Notify;