Handle RTCCertificate::fromPEM returning nullptr, with a unit test.

content/renderer/media/rtc_certificate_generator.cc

Index: content/renderer/media/rtc_certificate_generator.cc
diff --git a/content/renderer/media/rtc_certificate_generator.cc b/content/renderer/media/rtc_certificate_generator.cc
index 7ea08094a312e4d62e1a8c10911fcc09c693794e..bf1e2e22e97f5662274591377c7edab3da5590d9 100644
--- a/content/renderer/media/rtc_certificate_generator.cc
+++ b/content/renderer/media/rtc_certificate_generator.cc
@@ -166,8 +166,9 @@ std::unique_ptr<blink::WebRTCCertificate> RTCCertificateGenerator::fromPEM(
       rtc::RTCCertificate::FromPEM(
           rtc::RTCCertificatePEM(pem_private_key.utf8(),
               pem_certificate.utf8()));
-  return std::unique_ptr<blink::WebRTCCertificate>(
-      new RTCCertificate(certificate));
+  if (!certificate)
+    return nullptr;
+  return base::MakeUnique<RTCCertificate>(certificate);
 }
 
 }  // namespace content