[chromecast] Moves CastAudioOutputStream::Backend to CMA thread.

chromecast/media/cma/BUILD.gn

Index: chromecast/media/cma/BUILD.gn
diff --git a/chromecast/media/cma/BUILD.gn b/chromecast/media/cma/BUILD.gn
index 03b6384e3a972188ae7150730cdab16568757d31..2ba1312f49d460b2f0aca61f93666434c6166726 100644
--- a/chromecast/media/cma/BUILD.gn
+++ b/chromecast/media/cma/BUILD.gn
@@ -14,19 +14,9 @@ group("cma") {
   ]
 }
 
-source_set("unittests") {
+source_set("test_support") {
   testonly = true
   sources = [
-    "backend/audio_video_pipeline_device_unittest.cc",
-    "base/balanced_media_task_runner_unittest.cc",
-    "base/buffering_controller_unittest.cc",
-    "base/buffering_frame_provider_unittest.cc",
-    "base/decoder_buffer_adapter_unittest.cc",
-    "base/demuxer_stream_adapter_unittest.cc",
-    "base/demuxer_stream_for_test.cc",
-    "base/demuxer_stream_for_test.h",
-    "base/multi_demuxer_stream_adapter_unittest.cc",
-    "pipeline/audio_video_pipeline_impl_unittest.cc",
     "test/frame_generator_for_test.cc",
     "test/frame_generator_for_test.h",
     "test/frame_segmenter_for_test.cc",
@@ -37,28 +27,47 @@ source_set("unittests") {
     "test/mock_frame_provider.h",
     "test/mock_media_pipeline_backend.cc",
     "test/mock_media_pipeline_backend.h",
+    "test/mock_media_pipeline_backend_factory.cc",
+    "test/mock_media_pipeline_backend_factory.h",
   ]
 
   deps = [
     "//base",
-    "//base:i18n",
-    "//base/test:test_support",
-    "//chromecast/base",
-    "//chromecast/base/metrics:test_support",
-    "//chromecast/common/media:interfaces",
-    "//chromecast/media",
-    "//chromecast/media/audio",
     "//chromecast/media/cma/backend",
     "//chromecast/media/cma/base",
-    "//chromecast/media/cma/pipeline",
-    "//chromecast/public",
     "//media",
     "//media/base:test_support",
     "//testing/gmock",
     "//testing/gtest",
-    "//ui/display",
     "//ui/gfx/geometry",
   ]
+}
+
+source_set("unittests") {
+  testonly = true
+  sources = [
+    "backend/audio_video_pipeline_device_unittest.cc",
+    "base/balanced_media_task_runner_unittest.cc",
+    "base/buffering_controller_unittest.cc",
+    "base/buffering_frame_provider_unittest.cc",
+    "base/decoder_buffer_adapter_unittest.cc",
+    "base/demuxer_stream_adapter_unittest.cc",
+    "base/demuxer_stream_for_test.cc",
+    "base/demuxer_stream_for_test.h",
+    "base/multi_demuxer_stream_adapter_unittest.cc",
+    "pipeline/audio_video_pipeline_impl_unittest.cc",
+  ]
+
+  deps = [
+    ":test_support",
+    "//base",
+    "//base/test:test_support",
+    "//chromecast/base",
+    "//chromecast/media",
+    "//media",
+    "//testing/gmock",
+    "//testing/gtest",
+  ]
 
   data = [
     "//media/test/data/",