Refactor MediaResource to be multi-stream capable

media/base/media_resource.h

Index: media/base/media_resource.h
diff --git a/media/base/media_resource.h b/media/base/media_resource.h
index 2cd90192c013d892759f7ee2f939dfa31280d60f..9d911b3c3d8a7cbd6090eb16f20cb179a64ecca1 100644
--- a/media/base/media_resource.h
+++ b/media/base/media_resource.h
@@ -5,7 +5,11 @@
 #ifndef MEDIA_BASE_MEDIA_RESOURCE_H_
 #define MEDIA_BASE_MEDIA_RESOURCE_H_
 
+#include <vector>
+
+#include "base/callback.h"
 #include "base/macros.h"
+#include "base/time/time.h"
 #include "media/base/demuxer_stream.h"
 #include "media/base/media_export.h"
 #include "media/base/media_url_params.h"
@@ -13,6 +17,14 @@
 
 namespace media {
 
+// The callback that is used to notify clients about streams being enabled and
+// disabled. The first parameter is the DemuxerStream whose status changed. The
+// second parameter is a bool indicating whether the stream got enabled or
+// disabled. The third parameter specifies the media playback position at the
+// time the status change happened.
+using StreamStatusChangeCB =
+    base::RepeatingCallback<void(DemuxerStream*, bool, base::TimeDelta)>;
+
 // Abstract class that defines how to retrieve "media resources" in
 // DemuxerStream form (for most cases) or URL form (for the MediaPlayerRenderer
 // case).
@@ -30,9 +42,8 @@ class MEDIA_EXPORT MediaResource {
   virtual ~MediaResource();
 
   // For Type::STREAM:
-  //   Returns the first stream of the given stream type (which is not allowed
-  //   to be DemuxerStream::TEXT), or NULL if that type of stream is not
-  //   present.
+  // Returns a collection of available DemuxerStream objects. Note that some of
+  // those streams might be in disabled state (check DemuxerStream::enabled() ).
   //   NOTE: Once a DemuxerStream pointer is returned from GetStream it is
   //   guaranteed to stay valid for as long as the Demuxer/MediaResource
   //   is alive. But make no assumption that once GetStream returned a non-null
@@ -40,9 +51,7 @@ class MEDIA_EXPORT MediaResource {
   //   non-null pointer for the same stream type. In MSE Javascript code can
   //   remove SourceBuffer from a MediaSource at any point and this will make
   //   some previously existing streams inaccessible/unavailable.
-  // Other types:
-  //   Should not be called.
-  virtual DemuxerStream* GetStream(DemuxerStream::Type type) = 0;
+  virtual std::vector<DemuxerStream*> GetStreams() = 0;
 
   // For Type::URL:
   //   Returns the URL parameters of the media to play. Empty URLs are legal,
@@ -53,6 +62,10 @@ class MEDIA_EXPORT MediaResource {
 
   virtual MediaResource::Type GetType() const;
 
+  // The StreamStatusChangeCB allows clients to receive notifications about one
+  // of the streams being disabled or enabled.
+  virtual void SetStreamStatusChangeCB(const StreamStatusChangeCB& cb) = 0;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(MediaResource);
 };