Replace FFmpegDemuxer thread per element with base::TaskScheduler.

media/test/pipeline_integration_test.cc

Index: media/test/pipeline_integration_test.cc
diff --git a/media/test/pipeline_integration_test.cc b/media/test/pipeline_integration_test.cc
index 428a537242e98e2967ce318061072bcb4dcd0619..e5f294b9245bc1a1cb0808661baef348ac0ffef4 100644
--- a/media/test/pipeline_integration_test.cc
+++ b/media/test/pipeline_integration_test.cc
@@ -1731,16 +1731,12 @@ TEST_P(Mp3FastSeekIntegrationTest, FastSeekAccuracy_MP3) {
   EXPECT_HASH_EQ(config.hash, GetAudioHash());
 }
 
-// TODO(CHCUNNINGHAM): Re-enable for OSX once 1% flakiness is root caused.
-// See http://crbug.com/571898
-#if !defined(OS_MACOSX)
 // CBR seeks should always be fast and accurate.
 INSTANTIATE_TEST_CASE_P(
     CBRSeek_HasTOC,
     Mp3FastSeekIntegrationTest,
     ::testing::Values(Mp3FastSeekParams("bear-audio-10s-CBR-has-TOC.mp3",
-                                        "-0.71,0.36,2.96,2.68,2.10,-1.08,")));
-#endif
+                                        "-0.71,0.36,2.96,2.68,2.11,-1.08,")));
 
 INSTANTIATE_TEST_CASE_P(
     CBRSeeks_NoTOC,