Refactor: Renaming ssl_cert_chain to GetSSLCertificateChain()

Underscore methods in the middle of classes is against the chromium style guide
this change is part of a long series of changes to refactor crypto code in
WebRTC to conform to the chromium standard better.

1. ssl_cert() -> GetSSLCertificate()
2. ssl_cert_chain() -> GetSSLCertificateChain()
3. Small tidying up in rtccertificategenerator.cc

Bug: webrtc:9860
Change-Id: I670f76e31d6d4f873034edb72d958b3c227379cb
Reviewed-on: https://webrtc-review.googlesource.com/c/107802
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Benjamin Wright <benwright@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25371}
diff --git a/pc/statscollector.cc b/pc/statscollector.cc
index 23a4493..a1d52db 100644
--- a/pc/statscollector.cc
+++ b/pc/statscollector.cc
@@ -783,8 +783,8 @@
     StatsReport::Id local_cert_report_id, remote_cert_report_id;
     rtc::scoped_refptr<rtc::RTCCertificate> certificate;
     if (pc_->GetLocalCertificate(transport_name, &certificate)) {
-      StatsReport* r =
-          AddCertificateReports(certificate->ssl_cert_chain().GetStats());
+      StatsReport* r = AddCertificateReports(
+          certificate->GetSSLCertificateChain().GetStats());
       if (r)
         local_cert_report_id = r->id();
     }