reapply r70628. It was wrongly blamed for breaking Linux valgrind bots.

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 241fc049c8d9cfb4d2e10bd0c30b13c984586f92..14f15c6dc3ce55b0bdc4686a45c4eaea71e9cd0e 100644
--- a/net/disk_cache/disk_cache_perftest.cc
+++ b/net/disk_cache/disk_cache_perftest.cc
@@ -169,7 +169,7 @@ TEST_F(DiskCacheTest, CacheBackendPerformance) {
   disk_cache::Backend* cache;
   int rv = disk_cache::CreateCacheBackend(
                net::DISK_CACHE, test_cache.path(), 0, false,
-               cache_thread.message_loop_proxy(), &cache, &cb);
+               cache_thread.message_loop_proxy(), NULL, &cache, &cb);
 
   ASSERT_EQ(net::OK, cb.GetResult(rv));
 
@@ -198,7 +198,7 @@ TEST_F(DiskCacheTest, CacheBackendPerformance) {
 
   rv = disk_cache::CreateCacheBackend(net::DISK_CACHE, test_cache.path(), 0,
                                       false, cache_thread.message_loop_proxy(),
-                                      &cache, &cb);
+                                      NULL, &cache, &cb);
   ASSERT_EQ(net::OK, cb.GetResult(rv));
 
   ret = TimeRead(num_entries, cache, entries, true);