[Chromecast] Fix missing default stream volume.

This missing default can cause some audio streams to be muted by
default.

Bug: b/113075348
Test: Ran changes on developer device
Change-Id: Icaa75cf3d78a85f978b91dfa1de44d21b9266328
Reviewed-on: https://chromium-review.googlesource.com/1192114
Commit-Queue: Michael Nye <michaelnye@chromium.org>
Reviewed-by: Kenneth MacKay <kmackay@chromium.org>
Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589000}

chromecast/media/cma/backend/media_pipeline_backend_manager.cc

@@ -60,11 +60,18 @@ MediaPipelineBackendManager::MediaPipelineBackendManager(
           new base::ObserverListThreadSafe<AllowVolumeFeedbackObserver>()),
       global_volume_multipliers_({{AudioContentType::kMedia, 1.0f},
                                   {AudioContentType::kAlarm, 1.0f},
-                                  {AudioContentType::kCommunication, 1.0f}},
+                                  {AudioContentType::kCommunication, 1.0f},
+                                  {AudioContentType::kOther, 1.0f}},
                                  base::KEEP_FIRST_OF_DUPES),
       buffer_delegate_(nullptr),
       weak_factory_(this) {
   DCHECK(media_task_runner_);
+  DCHECK(playing_audio_streams_count_.size() ==
+         static_cast<unsigned long>(AudioContentType::kNumTypes));
+  DCHECK(playing_noneffects_audio_streams_count_.size() ==
+         static_cast<unsigned long>(AudioContentType::kNumTypes));
+  DCHECK(global_volume_multipliers_.size() ==
+         static_cast<unsigned long>(AudioContentType::kNumTypes));
   for (int i = 0; i < NUM_DECODER_TYPES; ++i) {
     decoder_count_[i] = 0;
   }

chromecast/public/volume_control.h

@@ -21,6 +21,7 @@ enum class AudioContentType {
   kAlarm,          // Alarm sounds.
   kCommunication,  // Voice communication, eg assistant TTS.
   kOther,          // No content type volume control (only per-stream control).
+  kNumTypes,       // Not a valid type; should always be last in the enum.
 };
 
 // Observer for volume/mute state changes. This is useful to detect volume