Use ScopedTaskEnvironment instead of MessageLoop in content unit tests.

content/browser/renderer_host/pepper/quota_reservation_unittest.cc

Index: content/browser/renderer_host/pepper/quota_reservation_unittest.cc
diff --git a/content/browser/renderer_host/pepper/quota_reservation_unittest.cc b/content/browser/renderer_host/pepper/quota_reservation_unittest.cc
index 7bed096cc039a51e4e895c39c477e5cf522bc240..fe4448b599ce4c375059e87c48c3f30928cfb806 100644
--- a/content/browser/renderer_host/pepper/quota_reservation_unittest.cc
+++ b/content/browser/renderer_host/pepper/quota_reservation_unittest.cc
@@ -17,6 +17,7 @@
 #include "base/macros.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 "storage/browser/fileapi/quota/quota_reservation.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -120,7 +121,7 @@ class QuotaReservationTest : public testing::Test {
   }
 
  private:
-  base::MessageLoop message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
   base::ScopedTempDir work_dir_;
   std::unique_ptr<storage::QuotaReservationManager> reservation_manager_;