Refactoring: move ownership of RtcEventLog from Call to PeerConnection

This CL is a pure refactoring which should not result in any functinal
changes. It moves ownership of the RtcEventLog from webrtc::Call to the
webrtc::PeerConnection object.

This is done so that we can add RtcEventLog support for ICE events -
which will require the TransportController to have a pointer to the
RtcEventLog. PeerConnection is the closest common owner of both Call and
TransportController (through WebRtcSession).

BUG=webrtc:6393

Review-Url: https://codereview.webrtc.org/2353033005
Cr-Commit-Position: refs/heads/master@{#14578}
diff --git a/webrtc/api/peerconnectionfactory.h b/webrtc/api/peerconnectionfactory.h
index 7684b95..7a30ab4 100644
--- a/webrtc/api/peerconnectionfactory.h
+++ b/webrtc/api/peerconnectionfactory.h
@@ -29,6 +29,8 @@
 
 namespace webrtc {
 
+class RtcEventLog;
+
 class PeerConnectionFactory : public PeerConnectionFactoryInterface {
  public:
   void SetOptions(const Options& options) override;
@@ -89,7 +91,8 @@
   void StopRtcEventLog() override {}
 
   virtual webrtc::MediaControllerInterface* CreateMediaController(
-      const cricket::MediaConfig& config) const;
+      const cricket::MediaConfig& config,
+      RtcEventLog* event_log) const;
   virtual cricket::TransportController* CreateTransportController(
       cricket::PortAllocator* port_allocator,
       bool redetermine_role_on_ice_restart);