By making RtcEventLogImpl's ctor public, we remove the necessity to make the function a friend. Visibility of RtcEventLogImpl is still limited to the .cc file.
BUG=webrtc:8111
Change-Id: I774d2e93620a8d9f24299ef2a94f7593b490839d
Reviewed-on: https://webrtc-review.googlesource.com/1237
Commit-Queue: Elad Alon <eladalon@webrtc.org>
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#19876}