Revert of Disable RTCVideoRenderFrameCallbackNV12 test

webrtc/sdk/objc/Framework/UnitTests/RTCMTLVideoViewTests.mm

 /*
  *  Copyright 2017 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 160 matching lines @@
 }
 
 TEST(RTCMTLVideoViewTests, RTCVideoRenderFrameCallbackI420) {
   RTCMTLVideoViewTests *test = [[RTCMTLVideoViewTests alloc] init];
   [test setup];
 
   [test testRTCVideoRenderFrameCallbackI420];
   [test tearDown];
 }
 
-// The test is disabled because of frequent crashes. See bugs.webrtc.org/7863
-TEST(RTCMTLVideoViewTests, DISABLED_RTCVideoRenderFrameCallbackNV12) {
+TEST(RTCMTLVideoViewTests, RTCVideoRenderFrameCallbackNV12) {
   RTCMTLVideoViewTests *test = [[RTCMTLVideoViewTests alloc] init];
   [test setup];
 
   [test testRTCVideoRenderFrameCallbackNV12];
   [test tearDown];
 }