[Chromecast] Limit number of concurrent audio and video decoders

chromecast/media/cma/backend/media_pipeline_backend_manager.h

Index: chromecast/media/cma/backend/media_pipeline_backend_manager.h
diff --git a/chromecast/media/cma/backend/media_pipeline_backend_manager.h b/chromecast/media/cma/backend/media_pipeline_backend_manager.h
index 54e6f205ad0e4d2cdfdbedb5c4fa01c2035ae031..1a4059c2298f8a293a16fe772749cee7e768a054 100644
--- a/chromecast/media/cma/backend/media_pipeline_backend_manager.h
+++ b/chromecast/media/cma/backend/media_pipeline_backend_manager.h
@@ -7,7 +7,6 @@
 
 #include <map>
 #include <memory>
-#include <vector>
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
@@ -49,15 +48,29 @@ class MediaPipelineBackendManager {
  private:
   friend class MediaPipelineBackendWrapper;
 
+  struct BackendInfo {
+    int audio_decoder_count_ = 0;
+    int video_decoder_count_ = 0;
+  };
+
+  // MediaPipelineBackendWrapper instances must check with these functions
+  // before creating decoders, so the manager can enforce global limits.
+  // If these return true, the count is incremented (i.e. it's assumed that the
+  // wrapper will create one).  It's decreased when backend is destroyed.
+  bool CanCreateAudioDecoder(MediaPipelineBackend* backend);
+  bool CanCreateVideoDecoder(MediaPipelineBackend* backend);
+
   // Internal clean up when a new media pipeline backend is destroyed.
-  void OnMediaPipelineBackendDestroyed(const MediaPipelineBackend* backend);
+  void OnMediaPipelineBackendDestroyed(MediaPipelineBackend* backend);
 
   float GetVolumeMultiplier(int stream_type);
 
   const scoped_refptr<base::SingleThreadTaskRunner> media_task_runner_;
 
-  // A vector that stores all of the existing media_pipeline_backends_.
-  std::vector<MediaPipelineBackend*> media_pipeline_backends_;
+  // Collection of all existing media_pipeline_backends_
+  std::map<MediaPipelineBackend*, BackendInfo> media_pipeline_backends_;
+  int audio_decoder_count_;
+  int video_decoder_count_;
 
   // Volume multiplier for each type of audio streams.
   std::map<int, float> volume_by_stream_type_;