Add thread safety documentation

An upcoming change will remove "synchronized" from the API docs. This change
documents those cases where the guarantees can be determined from code
inspection.

Bug: 25767152
Change-Id: I75083ce01513ed315222304fe3f34190d40748cb
diff --git a/core/java/android/net/LocalSocket.java b/core/java/android/net/LocalSocket.java
index a374a86..e14facb1 100644
--- a/core/java/android/net/LocalSocket.java
+++ b/core/java/android/net/LocalSocket.java
@@ -25,7 +25,8 @@
 
 /**
  * Creates a (non-server) socket in the UNIX-domain namespace. The interface
- * here is not entirely unlike that of java.net.Socket
+ * here is not entirely unlike that of java.net.Socket. This class and the streams
+ * returned from it may be used from multiple threads.
  */
 public class LocalSocket implements Closeable {