Check thread name for GL methods.

The thread name is used to verify the thread in both  createOpenGlObjectsAndInitializeFrameProcessors() and processFrame().
Also remove glThread field that was only used for this verification.

PiperOrigin-RevId: 437730804

libraries/transformer/src/main/java/androidx/media3/transformer/FrameProcessorChain.java

@@ -72,8 +72,6 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
   private final EGLContext eglContext;
   /** Some OpenGL commands may block, so all OpenGL commands are run on a background thread. */
   private final ExecutorService singleThreadExecutorService;
-  /** The {@link #singleThreadExecutorService} thread. */
-  private @MonotonicNonNull Thread glThread;
   /** Futures corresponding to the executor service's pending tasks. */
   private final ConcurrentLinkedQueue<Future<?>> futures;
   /** Number of frames {@link #registerInputFrame() registered} but not fully processed. */
@@ -355,7 +353,8 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
   @EnsuresNonNull("eglSurface")
   private Void createOpenGlObjectsAndInitializeFrameProcessors(
       Surface outputSurface, @Nullable SurfaceView debugSurfaceView) throws IOException {
-    glThread = Thread.currentThread();
+    checkState(Thread.currentThread().getName().equals(THREAD_NAME));
+
     if (enableExperimentalHdrEditing) {
       // TODO(b/209404935): Don't assume BT.2020 PQ input/output.
       eglSurface = GlUtil.getEglSurfaceBt2020Pq(eglDisplay, outputSurface);
@@ -396,7 +395,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
    */
   @RequiresNonNull({"inputSurfaceTexture", "eglSurface"})
   private void processFrame() {
-    checkState(Thread.currentThread().equals(glThread));
+    checkState(Thread.currentThread().getName().equals(THREAD_NAME));
 
     if (frameProcessors.isEmpty()) {
       GlUtil.focusEglSurface(eglDisplay, eglContext, eglSurface, outputWidth, outputHeight);