Remove traces of sequence_token_name in DebugLogWriter

Years ago DebugLogWriter used runners from SequencedWorkerPool to gather
and archive logs, thus requiring sequence_token_name argument to identify pool.

In b116e3b7 this was deprecated, work
migrated to TaskScheduler. But sequence_token_name argument persisted
and was passed into different methods without any real usage.

Also migrate from legacy Callback to OnceCallback.

Change-Id: If2b650fd6d7221be75002db28dd4afb46c14d6a5
Reviewed-on: https://chromium-review.googlesource.com/c/1480520Reviewed-by: Rahul Chaturvedi <rkc@chromium.org>
Reviewed-by: Denis Kuznetsov <antrim@chromium.org>
Commit-Queue: Oleg Davydov <burunduk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635935}

chrome/browser/chromeos/system_logs/debug_log_writer.h

@@ -16,7 +16,8 @@ class DebugLogWriter {
   // Called once StoreDebugLogs is complete. Takes two parameters:
   // - log_path: where the log file was saved in the case of success;
   // - succeeded: was the log file saved successfully.
-  typedef base::Callback<void(const base::FilePath& log_path, bool succeeded)>
+  typedef base::OnceCallback<void(const base::FilePath& log_path,
+                                  bool succeeded)>
       StoreLogsCallback;
 
   // Stores debug logs in either .tgz or .tar archive (depending on value of
@@ -26,14 +27,11 @@ class DebugLogWriter {
   // pool, prior to calling |callback|.
   static void StoreLogs(const base::FilePath& fileshelf,
                         bool should_compress,
-                        const StoreLogsCallback& callback);
+                        StoreLogsCallback callback);
 
   // Stores both system and user logs in .tgz archive on the |fileshelf|.
-  // |sequence_token_name| defines named sequence for task running on
-  // blocking pool (file operations).
   static void StoreCombinedLogs(const base::FilePath& fileshelf,
-                                const std::string& sequence_token_name,
-                                const StoreLogsCallback& callback);
+                                StoreLogsCallback callback);
 
  private:
   DebugLogWriter();