Use ReusableBufferedOutputStream for cache index file write operation

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=139889957

library/src/main/java/com/google/android/exoplayer2/upstream/cache/CachedContentIndex.java

@@ -20,9 +20,9 @@ import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.upstream.cache.Cache.CacheException;
 import com.google.android.exoplayer2.util.Assertions;
 import com.google.android.exoplayer2.util.AtomicFile;
+import com.google.android.exoplayer2.util.ReusableBufferedOutputStream;
 import com.google.android.exoplayer2.util.Util;
 import java.io.BufferedInputStream;
-import java.io.BufferedOutputStream;
 import java.io.DataInputStream;
 import java.io.DataOutputStream;
 import java.io.File;
@@ -61,6 +61,7 @@ import javax.crypto.spec.SecretKeySpec;
   private final Cipher cipher;
   private final SecretKeySpec secretKeySpec;
   private boolean changed;
+  private ReusableBufferedOutputStream bufferedOutputStream;
 
   /** Creates a CachedContentIndex which works on the index file in the given cacheDir. */
   public CachedContentIndex(File cacheDir) {
@@ -256,8 +257,13 @@ import javax.crypto.spec.SecretKeySpec;
   private void writeFile() throws CacheException {
     DataOutputStream output = null;
     try {
-      OutputStream outputStream = new BufferedOutputStream(atomicFile.startWrite());
-      output = new DataOutputStream(outputStream);
+      OutputStream outputStream = atomicFile.startWrite();
+      if (bufferedOutputStream == null) {
+        bufferedOutputStream = new ReusableBufferedOutputStream(outputStream);
+      } else {
+        bufferedOutputStream.reset(outputStream);
+      }
+      output = new DataOutputStream(bufferedOutputStream);
       output.writeInt(VERSION);
 
       int flags = cipher != null ? FLAG_ENCRYPTED_INDEX : 0;
@@ -274,7 +280,7 @@ import javax.crypto.spec.SecretKeySpec;
           throw new IllegalStateException(e); // Should never happen.
         }
         output.flush();
-        output = new DataOutputStream(new CipherOutputStream(outputStream, cipher));
+        output = new DataOutputStream(new CipherOutputStream(bufferedOutputStream, cipher));
       }
 
       output.writeInt(keyToContent.size());

library/src/main/java/com/google/android/exoplayer2/util/ReusableBufferedOutputStream.java

@@ -25,6 +25,8 @@ import java.io.OutputStream;
  */
 public final class ReusableBufferedOutputStream extends BufferedOutputStream {
 
+  private boolean closed;
+
   public ReusableBufferedOutputStream(OutputStream out) {
     super(out);
   }
@@ -35,13 +37,14 @@ public final class ReusableBufferedOutputStream extends BufferedOutputStream {
 
   @Override
   public void close() throws IOException {
+    closed = true;
+
     Throwable thrown = null;
     try {
       flush();
     } catch (Throwable e) {
       thrown = e;
     }
-
     try {
       out.close();
     } catch (Throwable e) {
@@ -49,8 +52,6 @@ public final class ReusableBufferedOutputStream extends BufferedOutputStream {
         thrown = e;
       }
     }
-    out = null;
-
     if (thrown != null) {
       Util.sneakyThrow(thrown);
     }
@@ -64,7 +65,8 @@ public final class ReusableBufferedOutputStream extends BufferedOutputStream {
    * @throws IllegalStateException If the stream isn't closed.
    */
   public void reset(OutputStream out) {
-    Assertions.checkState(this.out == null);
+    Assertions.checkState(closed);
     this.out = out;
+    closed = false;
   }
 }