Add support for mono input to the GVR extension

Issue: #2710

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=159082518

extensions/gvr/build.gradle

@@ -25,7 +25,7 @@ android {
 
 dependencies {
     compile project(':library-core')
-    compile 'com.google.vr:sdk-audio:1.30.0'
+    compile 'com.google.vr:sdk-audio:1.60.1'
 }
 
 ext {

extensions/gvr/src/main/java/com/google/android/exoplayer2/ext/gvr/GvrAudioProcessor.java

@@ -82,6 +82,9 @@ public final class GvrAudioProcessor implements AudioProcessor {
     maybeReleaseGvrAudioSurround();
     int surroundFormat;
     switch (channelCount) {
+      case 1:
+        surroundFormat = GvrAudioSurround.SurroundFormat.SURROUND_MONO;
+        break;
       case 2:
         surroundFormat = GvrAudioSurround.SurroundFormat.SURROUND_STEREO;
         break;