IBinder.transact: clarify return

False can't be returned for a oneway call.

Bug: N/A (from email thread)
Test: N/A
Change-Id: Ie2641877e30d00e7c5e195d763e361fd2992c963

core/java/android/os/IBinder.java

@@ -293,7 +293,10 @@ public interface IBinder {
      *
      * @return Returns the result from {@link Binder#onTransact}.  A successful call
      * generally returns true; false generally means the transaction code was not
-     * understood.
+     * understood.  For a oneway call to a different process false should never be
+     * returned.  If a oneway call is made to code in the same process (usually to
+     * a C++ or Rust implementation), then there are no oneway semantics, and
+     * false can still be returned.
      */
     public boolean transact(int code, @NonNull Parcel data, @Nullable Parcel reply, int flags)
         throws RemoteException;