[TaskEnvironment] Mass-migrate away from ScopedTaskEnvironment

(second half of
 https://chromium-review.googlesource.com/c/chromium/src/+/1756247)

This is step #1 of the mass migration. Some of these will be
backported to SingleThreadTaskEnvironment in a later phase.

scoped_task_environment.h will also only move in a follow-up CL.

TBR=dcheng@chromium.org

Bug: 992483
Change-Id: Ie80f083eeeb209180ab3c2884f1b566f73549cc6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1756248
Reviewed-by: Gabriel Charette <gab@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688142}

diff --git a/media/filters/decrypting_audio_decoder_unittest.cc b/media/filters/decrypting_audio_decoder_unittest.cc
index e1d52e6..87515ad 100644
--- a/media/filters/decrypting_audio_decoder_unittest.cc
+++ b/media/filters/decrypting_audio_decoder_unittest.cc

@@ -57,7 +57,7 @@
  public:
   DecryptingAudioDecoderTest()
       : decoder_(new DecryptingAudioDecoder(
-            scoped_task_environment_.GetMainThreadTaskRunner(),
+            task_environment_.GetMainThreadTaskRunner(),
             &media_log_)),
         cdm_context_(new StrictMock<MockCdmContext>()),
         decryptor_(new StrictMock<MockDecryptor>()),
@@ -244,7 +244,7 @@
 
   MOCK_METHOD1(OnWaiting, void(WaitingReason));
 
-  base::test::ScopedTaskEnvironment scoped_task_environment_;
+  base::test::TaskEnvironment task_environment_;
   NullMediaLog media_log_;
   std::unique_ptr<DecryptingAudioDecoder> decoder_;
   std::unique_ptr<StrictMock<MockCdmContext>> cdm_context_;