DropBoxManager: use BufferedInputStream when using GZIPInputStream

GZIPInputStream has a bug (b/195554062) where it uses unbuffered IO
when reading the gzip header.  This triggers the UnbufferedIoViolation
strict mode violation for apps that target API level 28+.

Independently of fixing GZIPInputStream, DropBoxManager can use
BufferedInputStream to take a proactive step against this and future
bugs.

Bug: 195554712
Test: Successfully read gzip dropbox entries from API level 28+ app.
Change-Id: Id539efcb366b3e3d53513a098975b25866ed16ff

core/java/android/os/DropBoxManager.java

@@ -30,6 +30,7 @@ import android.util.Log;
 
 import com.android.internal.os.IDropBoxManagerService;
 
+import java.io.BufferedInputStream;
 import java.io.ByteArrayInputStream;
 import java.io.Closeable;
 import java.io.File;
@@ -234,7 +235,8 @@ public class DropBoxManager {
             } else {
                 return null;
             }
-            return (mFlags & IS_GZIPPED) != 0 ? new GZIPInputStream(is) : is;
+            return (mFlags & IS_GZIPPED) != 0
+                ? new GZIPInputStream(new BufferedInputStream(is)) : is;
         }
 
         public static final @android.annotation.NonNull Parcelable.Creator<Entry> CREATOR = new Parcelable.Creator() {