Add GVR extension and GvrBufferProcessor.

A GvrBufferProcessor can be passed to the player by overriding SimpleExoPlayer's
buildBufferProcessors method.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=148442114

extensions/gvr/README.md

+# ExoPlayer GVR Extension #
+
+## Description ##
+
+The GVR extension wraps the [Google VR SDK for Android][]. It provides a
+GvrBufferProcessor, which uses [GvrAudioSurround][] to provide binaural
+rendering of surround sound and ambisonic soundfields.
+
+## Instructions ##
+
+If using SimpleExoPlayer, override SimpleExoPlayer.buildBufferProcessors to
+return a GvrBufferProcessor.
+
+If constructing renderers directly, pass a GvrBufferProcessor to
+MediaCodecAudioRenderer's constructor.
+
+[Google VR SDK for Android]: https://developers.google.com/vr/android/
+[GvrAudioSurround]: https://developers.google.com/vr/android/reference/com/google/vr/sdk/audio/GvrAudioSurround
+

extensions/gvr/build.gradle

+// Copyright (C) 2017 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+apply plugin: 'com.android.library'
+
+android {
+    compileSdkVersion project.ext.compileSdkVersion
+    buildToolsVersion project.ext.buildToolsVersion
+
+    defaultConfig {
+        // Required by com.google.vr:sdk-audio.
+        minSdkVersion 19
+        targetSdkVersion project.ext.targetSdkVersion
+    }
+}
+
+dependencies {
+    compile project(':library')
+    compile 'com.google.vr:sdk-audio:1.20.0'
+}

settings.gradle

@@ -15,20 +15,19 @@ include ':library'
 include ':testutils'
 include ':demo'
 include ':playbacktests'
+include ':extension-ffmpeg'
+include ':extension-flac'
+include ':extension-okhttp'
 include ':extension-opus'
 include ':extension-vp9'
-include ':extension-okhttp'
-include ':extension-flac'
-include ':extension-ffmpeg'
 // Uncomment the following line to use the Cronet Extension.
 // include ':extension-cronet'
 
-
+project(':extension-ffmpeg').projectDir = new File(settingsDir, 'extensions/ffmpeg')
+project(':extension-flac').projectDir = new File(settingsDir, 'extensions/flac')
+project(':extension-okhttp').projectDir = new File(settingsDir, 'extensions/okhttp')
 project(':extension-opus').projectDir = new File(settingsDir, 'extensions/opus')
 project(':extension-vp9').projectDir = new File(settingsDir, 'extensions/vp9')
-project(':extension-okhttp').projectDir = new File(settingsDir, 'extensions/okhttp')
-project(':extension-flac').projectDir = new File(settingsDir, 'extensions/flac')
-project(':extension-ffmpeg').projectDir = new File(settingsDir, 'extensions/ffmpeg')
 // Uncomment the following line to use the Cronet Extension.
 // See extensions/cronet/README.md for details.
 // project(':extension-cronet').projectDir = new File(settingsDir, 'extensions/cronet')