Do not DCHECK on SimpleCache deletion-while-closing.

net/disk_cache/backend_unittest.cc

Index: net/disk_cache/backend_unittest.cc
diff --git a/net/disk_cache/backend_unittest.cc b/net/disk_cache/backend_unittest.cc
index bb313ed39d2075d060f0f88ebdeb370d71143d5b..843a6199df700671fad43d253d30ebde381fe277 100644
--- a/net/disk_cache/backend_unittest.cc
+++ b/net/disk_cache/backend_unittest.cc
@@ -3481,3 +3481,15 @@ TEST_F(DiskCacheBackendTest, SimpleCacheEnumerationDestruction) {
   cache_.reset();
   // This test passes if we don't leak memory.
 }
+
+// Tests that a SimpleCache doesn't crash when files are deleted very quickly
+// after closing.
+// NOTE: IF THIS TEST IS FLAKY THEN IT IS FAILING. See https://crbug.com/416940
+TEST_F(DiskCacheBackendTest, SimpleCacheDeleteQuickly) {
+  SetSimpleCacheMode();
+  for (int i = 0; i < 100; ++i) {
+    InitCache();
+    cache_.reset();
+    EXPECT_TRUE(CleanupCacheDir());
+  }
+}