Task Scheduler API migration: change BrowserThreadModelWorker to SequencedModelWorker

BrowserThreads are being deprecated in favor of TaskScheduler API.
This change refactors BrowserThreadModelWorker preparing it to
run on a sequence rather than a browser thread.

Most of this change is a trivial renaming:
BrowserThreadModelWorker -> SequencedModelWorker
IsOnModelThread -> IsOnModelSequence

BUG=689520,731903

Review-Url: https://codereview.chromium.org/2942773002
Cr-Commit-Position: refs/heads/master@{#480569}
diff --git a/components/browser_sync/profile_sync_test_util.cc b/components/browser_sync/profile_sync_test_util.cc
index 5752712..c482bfb 100644
--- a/components/browser_sync/profile_sync_test_util.cc
+++ b/components/browser_sync/profile_sync_test_util.cc
@@ -16,8 +16,8 @@
 #include "components/signin/core/browser/signin_manager_base.h"
 #include "components/sync/base/sync_prefs.h"
 #include "components/sync/driver/signin_manager_wrapper.h"
-#include "components/sync/engine/browser_thread_model_worker.h"
 #include "components/sync/engine/passive_model_worker.h"
+#include "components/sync/engine/sequenced_model_worker.h"
 #include "components/sync/engine/ui_model_worker.h"
 #include "net/url_request/url_request_test_util.h"
 
@@ -130,10 +130,9 @@
   DCHECK(file_thread_) << "DB thread was specified but FILE thread was not.";
   switch (group) {
     case syncer::GROUP_DB:
-      return new syncer::BrowserThreadModelWorker(db_thread_, syncer::GROUP_DB);
+      return new syncer::SequencedModelWorker(db_thread_, syncer::GROUP_DB);
     case syncer::GROUP_FILE:
-      return new syncer::BrowserThreadModelWorker(file_thread_,
-                                                  syncer::GROUP_FILE);
+      return new syncer::SequencedModelWorker(file_thread_, syncer::GROUP_FILE);
     case syncer::GROUP_UI:
       return new syncer::UIModelWorker(base::ThreadTaskRunnerHandle::Get());
     case syncer::GROUP_PASSIVE: