Merge "doc getCallingPid zero return" into main

core/java/android/os/Binder.java

@@ -309,7 +309,11 @@ public class Binder implements IBinder {
      * If the current thread is not currently executing an incoming transaction,
      * then its own PID is returned.
      *
-     * Warning: oneway transactions do not receive PID.
+     * Warning: oneway transactions do not receive PID. Even if you expect
+     * a transaction to be synchronous, a misbehaving client could send it
+     * as a asynchronous call and result in a 0 PID here. Additionally, if
+     * there is a race and the calling process dies, the PID may still be
+     * 0 for a synchronous call.
      */
     @CriticalNative
     public static final native int getCallingPid();