Tests: Simplify SequencedWorkerPoolOwner, call Shutdown on destructor.

content/browser/net/quota_policy_cookie_store_unittest.cc

Index: content/browser/net/quota_policy_cookie_store_unittest.cc
diff --git a/content/browser/net/quota_policy_cookie_store_unittest.cc b/content/browser/net/quota_policy_cookie_store_unittest.cc
index f7987c553510e81966abfb12169d471cd0e0d1a8..ca33d6ecbd3185533d20dbc5a2797d0b9e809069 100644
--- a/content/browser/net/quota_policy_cookie_store_unittest.cc
+++ b/content/browser/net/quota_policy_cookie_store_unittest.cc
@@ -109,7 +109,6 @@ class QuotaPolicyCookieStoreTest : public testing::Test {
     // tasks that block pool shutdown (e.g. |store_|'s cleanup) have run before
     // yielding control.
     pool_owner_->pool()->FlushForTesting();
-    pool_owner_->pool()->Shutdown();
     pool_owner_.reset(new base::SequencedWorkerPoolOwner(3, "Background Pool"));
   }
 
@@ -119,7 +118,6 @@ class QuotaPolicyCookieStoreTest : public testing::Test {
 
   void TearDown() override {
     DestroyStore();
-    pool_owner_->pool()->Shutdown();
   }
 
   TestBrowserThreadBundle bundle_;