Add MMAP Audio Balance

Similar to adding Mono audio, this cl adds the audio balance settings
to MMAP Audio.

Bug:209521805
Test: Settings -> Accessibility -> Audio Adjustment -> Audio Balance
Use OboeTester and play outputs with various settings on the slider

Change-Id: I3269f6fe39b5f720da69739c49eb787e57f93b0a
diff --git a/media/libaaudio/src/client/AudioStreamInternal.cpp b/media/libaaudio/src/client/AudioStreamInternal.cpp
index 1b8e224..afdc2ac 100644
--- a/media/libaaudio/src/client/AudioStreamInternal.cpp
+++ b/media/libaaudio/src/client/AudioStreamInternal.cpp
@@ -272,12 +272,15 @@
     }
 
     // Exclusive output streams should combine channels when mono audio adjustment
-    // is enabled.
+    // is enabled. They should also adjust for audio balance.
     if ((getDirection() == AAUDIO_DIRECTION_OUTPUT) &&
         (getSharingMode() == AAUDIO_SHARING_MODE_EXCLUSIVE)) {
         bool isMasterMono = false;
         android::AudioSystem::getMasterMono(&isMasterMono);
         setRequireMonoBlend(isMasterMono);
+        float audioBalance = 0;
+        android::AudioSystem::getMasterBalance(&audioBalance);
+        setAudioBalance(audioBalance);
     }
 
     // For debugging and analyzing the distribution of MMAP timestamps.