Convert some SingleThreadTaskRunner => SequencedTaskRunner.

Change-Id: I3cc29edd1f2258348b07537909f86e4c9a1b69cc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2521168
Commit-Queue: Frank Liberato <liberato@chromium.org>
Auto-Submit: Frank Liberato <liberato@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825104}

diff --git a/media/filters/decrypting_media_resource.cc b/media/filters/decrypting_media_resource.cc
index 26bdaa0..b029b40 100644
--- a/media/filters/decrypting_media_resource.cc
+++ b/media/filters/decrypting_media_resource.cc

@@ -22,7 +22,7 @@
     MediaResource* media_resource,
     CdmContext* cdm_context,
     MediaLog* media_log,
-    scoped_refptr<base::SingleThreadTaskRunner> task_runner)
+    scoped_refptr<base::SequencedTaskRunner> task_runner)
     : media_resource_(media_resource),
       cdm_context_(cdm_context),
       media_log_(media_log),
@@ -33,7 +33,7 @@
   DCHECK(cdm_context_->GetDecryptor());
   DCHECK(cdm_context_->GetDecryptor()->CanAlwaysDecrypt());
   DCHECK(media_log_);
-  DCHECK(task_runner->BelongsToCurrentThread());
+  DCHECK(task_runner->RunsTasksInCurrentSequence());
 }
 
 DecryptingMediaResource::~DecryptingMediaResource() = default;