Refactor FileRotatingStream to use FileWrapper rather than FileStream

Bug: webrtc:6463
Change-Id: I77df2c77a658e9c5614554fb5ef8f2dc053031e6
Reviewed-on: https://webrtc-review.googlesource.com/c/117620
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26355}

rtc_base/stream.h

@@ -192,6 +192,7 @@ class StreamAdapterInterface : public StreamInterface,
 // support asynchronous notification.
 ///////////////////////////////////////////////////////////////////////////////
 
+// TODO(bugs.webrtc.org/6463): Delete this class.
 class FileStream : public StreamInterface {
  public:
   FileStream();