Use ScopedTaskEnvironment instead of MessageLoop in content unit tests.

content/browser/appcache/appcache_service_unittest.cc

Index: content/browser/appcache/appcache_service_unittest.cc
diff --git a/content/browser/appcache/appcache_service_unittest.cc b/content/browser/appcache/appcache_service_unittest.cc
index ee3dfdde9f9d546835f45b105a93cd4babd6ca8e..0f1c7f02e18bd84656d6385441039cb5e28d42bb 100644
--- a/content/browser/appcache/appcache_service_unittest.cc
+++ b/content/browser/appcache/appcache_service_unittest.cc
@@ -13,6 +13,7 @@
 #include "base/pickle.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
+#include "base/test/scoped_task_environment.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "content/browser/appcache/appcache_response.h"
 #include "content/browser/appcache/appcache_service_impl.h"
@@ -188,7 +189,7 @@ class AppCacheServiceImplTest : public testing::Test {
   net::CompletionCallback deletion_callback_;
 
  private:
-  base::MessageLoop message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
 };
 
 TEST_F(AppCacheServiceImplTest, DeleteAppCachesForOrigin) {