[scheduling] Use ScopedTaskEnvironment instead of MessageLoop in storage_monitor

MessageLoop will go away, eventually.

BUG=891670

Change-Id: Ic4740c19ad445bb1974f12876732829b88148a01
Reviewed-on: https://chromium-review.googlesource.com/c/1352782Reviewed-by: Tommy Li <tommycli@chromium.org>
Commit-Queue: Carlos Caballero <carlscab@google.com>
Cr-Commit-Position: refs/heads/master@{#612713}

components/storage_monitor/storage_monitor_unittest.cc

@@ -4,7 +4,6 @@
 
 #include "components/storage_monitor/storage_monitor.h"
 
-#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/synchronization/waitable_event.h"
@@ -24,7 +23,7 @@ void SetLatch(bool* called) {
 namespace storage_monitor {
 
 TEST(StorageMonitorTest, TestInitialize) {
-  base::MessageLoop message_loop;
+  base::test::ScopedTaskEnvironment task_environment;
   TestStorageMonitor::Destroy();
   TestStorageMonitor monitor;
   EXPECT_FALSE(monitor.init_called());
@@ -39,7 +38,7 @@ TEST(StorageMonitorTest, TestInitialize) {
 
 TEST(StorageMonitorTest, DeviceAttachDetachNotifications) {
   TestStorageMonitor::Destroy();
-  base::MessageLoop message_loop;
+  base::test::ScopedTaskEnvironment task_environment;
   const std::string kDeviceId1 = "dcim:UUID:FFF0-0001";
   const std::string kDeviceId2 = "dcim:UUID:FFF0-0002";
   MockRemovableStorageObserver observer1;
@@ -82,7 +81,7 @@ TEST(StorageMonitorTest, DeviceAttachDetachNotifications) {
 
 TEST(StorageMonitorTest, GetAllAvailableStoragesEmpty) {
   TestStorageMonitor::Destroy();
-  base::MessageLoop message_loop;
+  base::test::ScopedTaskEnvironment task_environment;
   TestStorageMonitor monitor;
   std::vector<StorageInfo> devices = monitor.GetAllAvailableStorages();
   EXPECT_EQ(0U, devices.size());
@@ -90,7 +89,7 @@ TEST(StorageMonitorTest, GetAllAvailableStoragesEmpty) {
 
 TEST(StorageMonitorTest, GetAllAvailableStorageAttachDetach) {
   TestStorageMonitor::Destroy();
-  base::MessageLoop message_loop;
+  base::test::ScopedTaskEnvironment task_environment;
   TestStorageMonitor monitor;
   const std::string kDeviceId1 = "dcim:UUID:FFF0-0042";
   const base::FilePath kDevicePath1(FILE_PATH_LITERAL("/testfoo"));