Add TaskPriority as a parameter to SequencedWorkerPool in preparation for TaskScheduler experiment.

net/disk_cache/blockfile/file_posix.cc

Index: net/disk_cache/blockfile/file_posix.cc
diff --git a/net/disk_cache/blockfile/file_posix.cc b/net/disk_cache/blockfile/file_posix.cc
index 5a3ad455478f65cd844a6c49ca28c1e1e36cb45f..cdde5b0d45e73e4782ef493046dfb70a547cb1d3 100644
--- a/net/disk_cache/blockfile/file_posix.cc
+++ b/net/disk_cache/blockfile/file_posix.cc
@@ -25,7 +25,10 @@ const int kMaxThreads = 5;
 
 class FileWorkerPool : public base::SequencedWorkerPool {
  public:
-  FileWorkerPool() : base::SequencedWorkerPool(kMaxThreads, "CachePool") {}
+  FileWorkerPool()
+      : base::SequencedWorkerPool(kMaxThreads,
+                                  "CachePool",
+                                  base::TaskPriority::USER_BLOCKING) {}
 
  protected:
   ~FileWorkerPool() override {}