Sequence[d]TaskRunner

Fix documentation misspellings.

BUG=none

Review-Url: https://codereview.chromium.org/2959563002
Cr-Commit-Position: refs/heads/master@{#482456}
diff --git a/docs/threading_and_tasks.md b/docs/threading_and_tasks.md
index b29e601..6cc56bdc 100644
--- a/docs/threading_and_tasks.md
+++ b/docs/threading_and_tasks.md
@@ -656,11 +656,11 @@
  public:
 
   void SetBackgroundTaskRunnerForTesting(
-      scoped_refptr<base::SequenceTaskRunner> background_task_runner);
+      scoped_refptr<base::SequencedTaskRunner> background_task_runner);
 
  private:
-  scoped_refptr<base::SequenceTaskRunner> background_task_runner_ =
-      base::CreateSequenceTaskRunnerWithTraits(
+  scoped_refptr<base::SequencedTaskRunner> background_task_runner_ =
+      base::CreateSequencedTaskRunnerWithTraits(
           {base::MayBlock(), base::TaskPriority::BACKGROUND});
 }
 ```