device/bluetooth: Add I/O watcher for audio data retrieval triggered by state change.

chromeos/dbus/bluetooth_media_transport_client.cc

Index: chromeos/dbus/bluetooth_media_transport_client.cc
diff --git a/chromeos/dbus/bluetooth_media_transport_client.cc b/chromeos/dbus/bluetooth_media_transport_client.cc
index 2be8a5639efa46f7f140eb62af71d1f91a0db2ad..e8b06ee3e750d9f596bbc58f7edfae34a64431a1 100644
--- a/chromeos/dbus/bluetooth_media_transport_client.cc
+++ b/chromeos/dbus/bluetooth_media_transport_client.cc
@@ -241,7 +241,16 @@ class BluetoothMediaTransportClientImpl
     if (reader.PopFileDescriptor(&fd) &&
         reader.PopUint16(&read_mtu) &&
         reader.PopUint16(&write_mtu)) {
-      callback.Run(fd, read_mtu, write_mtu);
+      fd.CheckValidity();
+      DCHECK(fd.is_valid());
+
+      VLOG(1) << "OnAcquireSuccess - fd: "<<  fd.value()
+              <<", read MTU: " << read_mtu
+              <<", write MTU: " << write_mtu;
+
+      // The ownership of the file descriptor is transferred to the user
+      // application.
+      callback.Run(fd.TakeValue(), read_mtu, write_mtu);

[armansito, 2015/03/12 03:42:54]

You don't want to do this here, I would leave it up to the caller of Acquire to
take ownership of the file descriptor. The problem is, if you call TakeValue
here and the caller of Acquire doesn't do anything with it, the file descriptor
would never be closed and hence get leaked. Instead, I would just return a
pointer to the dbus::FileDescriptor class and let the caller explicitly take
ownership of the fd.

[Miao, 2015/03/12 22:33:31]

Done.

       return;
     }