Marks ConditionVariable as non-final so it can be mocked.

PiperOrigin-RevId: 291207668

library/core/src/main/java/com/google/android/exoplayer2/util/ConditionVariable.java

@@ -19,7 +19,7 @@ package com.google.android.exoplayer2.util;
  * An interruptible condition variable whose {@link #open()} and {@link #close()} methods return
  * An interruptible condition variable whose {@link #open()} and {@link #close()} methods return
  * whether they resulted in a change of state.
  * whether they resulted in a change of state.
  */
  */
-public final class ConditionVariable {
+public class ConditionVariable {
 
 
   private boolean isOpen;
   private boolean isOpen;