Update exoplayer 1 and 2 to support stereo mesh layout.

Reference spec:
https://github.com/google/spatial-media/blob/master/docs/spherical-video-v2-rfc.md#semantics

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=147060701

library/src/main/java/com/google/android/exoplayer2/C.java

@@ -515,7 +515,13 @@ public final class C {
    * The stereo mode for 360/3D/VR videos.
    */
   @Retention(RetentionPolicy.SOURCE)
-  @IntDef({Format.NO_VALUE, STEREO_MODE_MONO, STEREO_MODE_TOP_BOTTOM, STEREO_MODE_LEFT_RIGHT})
+  @IntDef({
+      Format.NO_VALUE,
+      STEREO_MODE_MONO,
+      STEREO_MODE_TOP_BOTTOM,
+      STEREO_MODE_LEFT_RIGHT,
+      STEREO_MODE_STEREO_MESH
+  })
   public @interface StereoMode {}
   /**
    * Indicates Monoscopic stereo layout, used with 360/3D/VR videos.
@@ -529,6 +535,11 @@ public final class C {
    * Indicates Left-Right stereo layout, used with 360/3D/VR videos.
    */
   public static final int STEREO_MODE_LEFT_RIGHT = 2;
+  /**
+   * Indicates a stereo layout where the left and right eyes have separate meshes,
+   * used with 360/3D/VR videos.
+   */
+  public static final int STEREO_MODE_STEREO_MESH = 3;
 
   /**
    * Converts a time in microseconds to the corresponding time in milliseconds, preserving

library/src/main/java/com/google/android/exoplayer2/Format.java

@@ -120,7 +120,7 @@ public final class Format implements Parcelable {
   /**
    * The stereo layout for 360/3D/VR video, or {@link #NO_VALUE} if not applicable. Valid stereo
    * modes are {@link C#STEREO_MODE_MONO}, {@link C#STEREO_MODE_TOP_BOTTOM}, {@link
-   * C#STEREO_MODE_LEFT_RIGHT}.
+   * C#STEREO_MODE_LEFT_RIGHT}, {@link C#STEREO_MODE_STEREO_MESH}.
    */
   @C.StereoMode
   public final int stereoMode;

library/src/main/java/com/google/android/exoplayer2/extractor/mkv/MatroskaExtractor.java

@@ -673,6 +673,9 @@ public final class MatroskaExtractor implements Extractor {
           case 3:
             currentTrack.stereoMode = C.STEREO_MODE_TOP_BOTTOM;
             break;
+          case 15:
+            currentTrack.stereoMode = C.STEREO_MODE_STEREO_MESH;
+            break;
           default:
             break;
         }

library/src/main/java/com/google/android/exoplayer2/extractor/mp4/AtomParsers.java

@@ -720,6 +720,9 @@ import java.util.List;
             case 2:
               stereoMode = C.STEREO_MODE_LEFT_RIGHT;
               break;
+            case 3:
+              stereoMode = C.STEREO_MODE_STEREO_MESH;
+              break;
             default:
               break;
           }