Pass underlying volume UUID to StorageVolume.

To help MediaProvider uniquely identify storage devices, pass through
the UUID of the underlying private storage volume.

Bug: 23329611
Change-Id: I22ee7ea98fcb208d7797310acb3396a3f074f09b
diff --git a/core/java/android/os/storage/VolumeInfo.java b/core/java/android/os/storage/VolumeInfo.java
index ef54d84..6888594 100644
--- a/core/java/android/os/storage/VolumeInfo.java
+++ b/core/java/android/os/storage/VolumeInfo.java
@@ -341,6 +341,7 @@
         }
 
         String description = null;
+        String derivedFsUuid = fsUuid;
         long mtpReserveSize = 0;
         long maxFileSize = 0;
         int mtpStorageId = StorageVolume.STORAGE_ID_INVALID;
@@ -351,6 +352,7 @@
             final VolumeInfo privateVol = storage.findPrivateForEmulated(this);
             if (privateVol != null) {
                 description = storage.getBestVolumeDescription(privateVol);
+                derivedFsUuid = privateVol.fsUuid;
             }
 
             if (isPrimary()) {
@@ -393,7 +395,7 @@
 
         return new StorageVolume(id, mtpStorageId, userPath, description, isPrimary(), removable,
                 emulated, mtpReserveSize, allowMassStorage, maxFileSize, new UserHandle(userId),
-                fsUuid, envState);
+                derivedFsUuid, envState);
     }
 
     public static int buildStableMtpStorageId(String fsUuid) {