Make ANW.setSwapInterval(0) work again

we can now queue/dequeue a buffer in asynchrnous mode by using the
async parameter to these calls. async mode is only specified
with those calls (it is not modal anymore).

as a consequence it can only be specified when the buffer count
is not overidden, as error is returned otherwise.

Change-Id: Ic63f4f96f671cb9d65c4cecbcc192615e09a8b6b
diff --git a/include/gui/Surface.h b/include/gui/Surface.h
index 6f12e77..2f7406e 100644
--- a/include/gui/Surface.h
+++ b/include/gui/Surface.h
@@ -235,6 +235,10 @@
     // by the application
     bool mProducerControlledByApp;
 
+    // mSwapIntervalZero set if we should drop buffers at queue() time to
+    // achieve an asynchronous swap interval
+    bool mSwapIntervalZero;
+
     // mConsumerRunningBehind whether the consumer is running more than
     // one buffer behind the producer.
     mutable bool mConsumerRunningBehind;