Remove CircularFileStream / replace it with CallSessionFileRotatingStream.

BUG=4838, 4839

Review URL: https://codereview.webrtc.org/1245143005

Cr-Commit-Position: refs/heads/master@{#9628}
diff --git a/webrtc/base/logsinks.h b/webrtc/base/logsinks.h
index f86bdd0..849e1dc 100644
--- a/webrtc/base/logsinks.h
+++ b/webrtc/base/logsinks.h
@@ -39,6 +39,9 @@
   // Deletes any existing files in the directory and creates a new log file.
   virtual bool Init();
 
+  // Disables buffering on the underlying stream.
+  bool DisableBuffering();
+
  protected:
   explicit FileRotatingLogSink(FileRotatingStream* stream);
 
@@ -57,8 +60,6 @@
   ~CallSessionFileRotatingLogSink() override;
 
  private:
-  scoped_ptr<CallSessionFileRotatingStream> stream_;
-
   DISALLOW_COPY_AND_ASSIGN(CallSessionFileRotatingLogSink);
 };