Use ffmpeg for opus decoding, no need to maintain our decoder.

media/test/pipeline_integration_test.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <memory>
 #include <utility>
 
@@ skipping 1583 matching lines @@
 
   Play();
   EXPECT_TRUE(WaitUntilOnEnded());
 
   EXPECT_EQ(592, source.last_timestamp_offset().InMilliseconds());
   EXPECT_EQ(1u, pipeline_->GetBufferedTimeRanges().size());
   EXPECT_EQ(0, pipeline_->GetBufferedTimeRanges().start(0).InMilliseconds());
   EXPECT_EQ(592, pipeline_->GetBufferedTimeRanges().end(0).InMilliseconds());
 
   // Verify preroll is stripped.
-  EXPECT_HASH_EQ("-0.06,0.97,-0.90,-0.70,-0.53,-0.34,", GetAudioHash());
+  EXPECT_HASH_EQ("-0.25,0.67,0.04,0.14,-0.49,-0.41,", GetAudioHash());
 }
 
 TEST_F(PipelineIntegrationTest, BasicPlaybackHashed_MP3) {
   ASSERT_EQ(PIPELINE_OK, Start("sfx.mp3", kHashed));
 
   Play();
 
   ASSERT_TRUE(WaitUntilOnEnded());
 
   // Verify codec delay and preroll are stripped.
@@ skipping 893 matching lines @@
 
 TEST_F(PipelineIntegrationTest, BasicPlaybackPositiveStartTime) {
   ASSERT_EQ(PIPELINE_OK, Start("nonzero-start-time.webm"));
   Play();
   ASSERT_TRUE(WaitUntilOnEnded());
   ASSERT_EQ(base::TimeDelta::FromMicroseconds(396000),
             demuxer_->GetStartTime());
 }
 
 }  // namespace media