Change who allocated the MediaPipe's shared buffer.

mojo/services/media/common/interfaces/media_pipe.mojom

Index: mojo/services/media/common/interfaces/media_pipe.mojom
diff --git a/mojo/services/media/common/interfaces/media_pipe.mojom b/mojo/services/media/common/interfaces/media_pipe.mojom
index ca5e400ef54bef9563b52f70b89ed4fe99fc59a6..7efbd2fd7a6851d9df2474c3e99f52d1525f7ab5 100644
--- a/mojo/services/media/common/interfaces/media_pipe.mojom
+++ b/mojo/services/media/common/interfaces/media_pipe.mojom
@@ -61,25 +61,6 @@ struct MediaPacket {
   // packet?
 };
 
-// MediaPipeState
-//
-// A small structure used by the user of a media pipe to fetch the shared buffer
-// used by the media pipe to move bulk data.
-//
-// TODO(johngro): Right now, the only real purpose for this struture is to
-// bundle the size of the buffer with the buffer handle itself.  When buffer
-// handles can have their properties queried directly, it can go away.  See
-// domokit/mojo issue #501
-struct MediaPipeState {
-  const uint64 kMaxPayloadLen = 0x3FFFFFFFFFFFFFFF;
-
-  handle<shared_buffer> payload_buffer;
-
-  // TODO(johngro) : Why do I have to send this?  Why can't I just query the
-  // shared_buffer handle for its length?
-  uint64 payload_buffer_len;
-};
-
 // MediaPipe
 //
 // An interface exposed by consumers of media which provides the means for
@@ -90,6 +71,8 @@ struct MediaPipeState {
 // the media has been consumed via the SendPacket callback they provide.
 // Finally, the pipeline may be flushed using the Flush method.
 interface MediaPipe {
+  const uint64 kMaxBufferLen = 0x3FFFFFFFFFFFFFFF;
+
   // An enumeration used to indicate the ultimate fate of packets sent across
   // the pipe using the SendPacket method.
   enum SendResult {
@@ -97,9 +80,8 @@ interface MediaPipe {
     FLUSHED,   // Some or all of the media was flushed before being consumed.
   };
 
-  // Request that a reference to the pipe's state be sent to the caller via
-  // callback.
-  GetState() => (MediaPipeState state);
+  // Sets the shared buffer in which sent Packet payloads will be located.
+  SetBuffer(handle<shared_buffer> buffer, uint64 size);
 
   // Place a media packet into the pipeline to be consumed.  When the consumer
   // is finished with the packet, it will invoke the supplied callback to