aaudio: lower latency using MMAP capture

MMAP can be enabled by setting system properties.

Bug: 38267780
Test: input_monitor.cpp
Change-Id: I5e86fd1d9baef4fe59837ccbca7971acbb54d8b5
Signed-off-by: Phil Burk <philburk@google.com>
diff --git a/media/libaaudio/src/legacy/AudioStreamTrack.h b/media/libaaudio/src/legacy/AudioStreamTrack.h
index 186a08e..990f005 100644
--- a/media/libaaudio/src/legacy/AudioStreamTrack.h
+++ b/media/libaaudio/src/legacy/AudioStreamTrack.h
@@ -63,6 +63,10 @@
 
     int64_t getFramesRead() override;
 
+    aaudio_direction_t getDirection() const override {
+        return AAUDIO_DIRECTION_OUTPUT;
+    }
+
     aaudio_result_t updateStateWhileWaiting() override;
 
     // This is public so it can be called from the C callback function.