SSLCertificate basic fuzzer.

This change simply calls through all code paths in the SSLCertificate interface
after passing in an untrusted PEM string. Corpus will follow in another CL.

Bug: webrtc:10395
Change-Id: I001642fa89a84ce01505780f5e76f01a0e46a785
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/127640
Commit-Queue: Benjamin Wright <benwright@webrtc.org>
Reviewed-by: Steve Anton <steveanton@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27118}

test/fuzzers/BUILD.gn

@@ -619,3 +619,12 @@ webrtc_fuzzer_test("rtp_header_parser_fuzzer") {
     "../../modules/rtp_rtcp",
   ]
 }
+
+webrtc_fuzzer_test("ssl_certificate_fuzzer") {
+  sources = [
+    "rtp_header_parser_fuzzer.cc",
+  ]
+  deps = [
+    "../../modules/rtp_rtcp",
+  ]
+}

test/fuzzers/ssl_certificate_fuzzer.cc

@@ -0,0 +1,47 @@
+/*
+ *  Copyright (c) 2019 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include <stddef.h>
+#include <stdint.h>
+#include <string>
+
+#include "rtc_base/ssl_certificate.h"
+#include "rtc_base/string_encode.h"
+
+namespace webrtc {
+
+void FuzzOneInput(const uint8_t* data, size_t size) {
+  std::string pem_certificate(reinterpret_cast<const char*>(data), size);
+
+  std::unique_ptr<rtc::SSLCertificate> cert =
+      rtc::SSLCertificate::FromPEMString(pem_certificate);
+
+  if (cert == nullptr) {
+    return;
+  }
+
+  cert->Clone();
+  cert->GetStats();
+  cert->ToPEMString();
+  cert->CertificateExpirationTime();
+
+  std::string algorithm;
+  cert->GetSignatureDigestAlgorithm(algorithm);
+
+  unsigned char digest[rtc::MessageDigest::kMaxSize];
+  size_t digest_len;
+  cert->ComputeDigest(algorithm, digest, rtc::MessageDigest::kMaxSize,
+                      &digest_len);
+
+  rtc::Buffer der_buffer;
+  cert->ToDER(&der_buffer);
+}
+
+}  // namespace webrtc