rollup merge of #22210: aturon/stab-final-borrow

Conflicts:
	src/libcollections/btree/map.rs
	src/libcollections/str.rs
	src/libcollections/vec.rs
	src/libcore/borrow.rs
	src/libcore/hash/mod.rs
	src/libstd/collections/hash/map.rs
	src/libstd/collections/hash/set.rs

src/libstd/path.rs

@@ -108,12 +108,11 @@
 use core::prelude::*;
 
 use ascii::*;
-use borrow::BorrowFrom;
+use borrow::{Borrow, ToOwned, Cow};
 use cmp;
 use iter::{self, IntoIterator};
 use mem;
 use ops::{self, Deref};
-use string::CowString;
 use vec::Vec;
 use fmt;
 
@@ -982,12 +981,17 @@ impl ops::Deref for PathBuf {
     }
 }
 
-impl BorrowFrom<PathBuf> for Path {
-    fn borrow_from(owned: &PathBuf) -> &Path {
-        owned.deref()
+impl Borrow<Path> for PathBuf {
+    fn borrow(&self) -> &Path {
+        self.deref()
     }
 }
 
+impl ToOwned for Path {
+    type Owned = PathBuf;
+    fn to_owned(&self) -> PathBuf { self.to_path_buf() }
+}
+
 impl cmp::PartialEq for PathBuf {
     fn eq(&self, other: &PathBuf) -> bool {
         self.components() == other.components()
@@ -1066,10 +1070,10 @@ impl Path {
         self.inner.to_str()
     }
 
-    /// Convert a `Path` to a `CowString`.
+    /// Convert a `Path` to a `Cow<str>`.
     ///
     /// Any non-Unicode sequences are replaced with U+FFFD REPLACEMENT CHARACTER.
-    pub fn to_string_lossy(&self) -> CowString {
+    pub fn to_string_lossy(&self) -> Cow<str> {
         self.inner.to_string_lossy()
     }