Restore disk_cache perf tests runnability.

net/disk_cache/disk_cache_perftest.cc

Index: net/disk_cache/disk_cache_perftest.cc
diff --git a/net/disk_cache/disk_cache_perftest.cc b/net/disk_cache/disk_cache_perftest.cc
index e16cccb4fe41e53a501023b15ca3d878a5ca8742..5151d3492543b1219c32bcc0f7dca977e15e7891 100644
--- a/net/disk_cache/disk_cache_perftest.cc
+++ b/net/disk_cache/disk_cache_perftest.cc
@@ -15,6 +15,7 @@
 #include "base/run_loop.h"
 #include "base/strings/string_util.h"
 #include "base/test/perf_time_logger.h"
+#include "base/test/scoped_task_environment.h"
 #include "base/test/test_file_util.h"
 #include "base/threading/thread.h"
 #include "net/base/cache_type.h"
@@ -91,6 +92,7 @@ class DiskCachePerfTest : public DiskCacheTestWithCache {
 
  private:
   const size_t saved_fd_limit_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
 };
 
 // Creates num_entries on the cache, and writes kHeaderSize bytes of metadata