Use ScopedTaskEnvironment instead of MessageLoop in media/capture/ unit tests

media/capture/video/fake_video_capture_device_unittest.cc

Index: media/capture/video/fake_video_capture_device_unittest.cc
diff --git a/media/capture/video/fake_video_capture_device_unittest.cc b/media/capture/video/fake_video_capture_device_unittest.cc
index 2af74e7a3eb130bf0892f94f1a5cd764a148ea2f..90968827206e44eec856de1823ab7f63b226980c 100644
--- a/media/capture/video/fake_video_capture_device_unittest.cc
+++ b/media/capture/video/fake_video_capture_device_unittest.cc
@@ -14,6 +14,7 @@
 #include "base/command_line.h"
 #include "base/memory/ptr_util.h"
 #include "base/run_loop.h"
+#include "base/test/scoped_task_environment.h"
 #include "base/test/test_timeouts.h"
 #include "base/threading/thread.h"
 #include "build/build_config.h"
@@ -199,8 +200,7 @@ class ImageCaptureClient : public base::RefCounted<ImageCaptureClient> {
 class FakeVideoCaptureDeviceBase : public ::testing::Test {
  protected:
   FakeVideoCaptureDeviceBase()
-      : loop_(new base::MessageLoop()),
-        descriptors_(new VideoCaptureDeviceDescriptors()),
+      : descriptors_(new VideoCaptureDeviceDescriptors()),
         client_(CreateClient()),
         image_capture_client_(new ImageCaptureClient()),
         video_capture_device_factory_(new FakeVideoCaptureDeviceFactory()) {}
@@ -224,7 +224,7 @@ class FakeVideoCaptureDeviceBase : public ::testing::Test {
 
   const VideoCaptureFormat& last_format() const { return last_format_; }
 
-  const std::unique_ptr<base::MessageLoop> loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
   std::unique_ptr<VideoCaptureDeviceDescriptors> descriptors_;
   std::unique_ptr<base::RunLoop> run_loop_;
   std::unique_ptr<MockClient> client_;