Use ScopedTaskEnvironment instead of MessageLoop in /chromecast/media

MessageLoop will go away, eventually.

ScopedTaskEnvironment will per default start a ThreadPool, which should
be fine in most of the cases. If you belive your test needs to make sure
that no ThreadPool runs let me know and I will update the patch.

BUG=891670
This CL was uploaded by git cl split.

R=kmackay@chromium.org

Change-Id: I1ac52d598e71f6569f544c0cdaee67c07ffd7f1f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1648269
Auto-Submit: Carlos Caballero <carlscab@google.com>
Reviewed-by: Kenneth MacKay <kmackay@chromium.org>
Commit-Queue: Carlos Caballero <carlscab@google.com>
Cr-Commit-Position: refs/heads/master@{#669598}

chromecast/media/base/media_resource_tracker_unittest.cc

@@ -7,8 +7,8 @@
 #include <memory>
 
 #include "base/bind.h"
-#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
+#include "base/test/scoped_task_environment.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -62,8 +62,8 @@ class MediaResourceTrackerTest : public ::testing::Test {
     test_mocks_.reset(new MediaResourceTrackerTestMocks());
 
     resource_tracker_ = new TestMediaResourceTracker(
-        test_mocks_.get(), message_loop_.task_runner(),
-        message_loop_.task_runner());
+        test_mocks_.get(), scoped_task_environment_.GetMainThreadTaskRunner(),
+        scoped_task_environment_.GetMainThreadTaskRunner());
   }
 
   void InitializeMediaLib() {
@@ -72,7 +72,7 @@ class MediaResourceTrackerTest : public ::testing::Test {
     base::RunLoop().RunUntilIdle();
   }
 
-  base::MessageLoop message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
   TestMediaResourceTracker* resource_tracker_;
   std::unique_ptr<MediaResourceTrackerTestMocks> test_mocks_;
 

chromecast/media/cma/backend/multizone_backend_unittest.cc

@@ -15,8 +15,8 @@
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
-#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
+#include "base/test/scoped_task_environment.h"
 #include "base/threading/thread_checker.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/time/time.h"
@@ -152,7 +152,7 @@ class MultizoneBackendTest : public testing::TestWithParam<TestParams> {
   void OnEndOfStream();
 
  private:
-  base::MessageLoop message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
   std::vector<std::unique_ptr<BufferFeeder>> effects_feeders_;
   std::unique_ptr<BufferFeeder> audio_feeder_;