Switch to use SHA-256 for certificates / fingerprints.

This CL changes identity generation to use SHA-256 for the self-signed
certificates and the fingerprints sent in the SDP.

BUG=4602
R=juberti@google.com

Review URL: https://webrtc-codereview.appspot.com/47149004

Cr-Commit-Position: refs/heads/master@{#9173}
diff --git a/webrtc/base/sslidentity_unittest.cc b/webrtc/base/sslidentity_unittest.cc
index 3f756ef..fd75411 100644
--- a/webrtc/base/sslidentity_unittest.cc
+++ b/webrtc/base/sslidentity_unittest.cc
@@ -60,13 +60,13 @@
   void TestGetSignatureDigestAlgorithm() {
     std::string digest_algorithm;
     // Both NSSIdentity::Generate and OpenSSLIdentity::Generate are
-    // hard-coded to generate RSA-SHA1 certificates.
+    // hard-coded to generate RSA-SHA256 certificates.
     ASSERT_TRUE(identity1_->certificate().GetSignatureDigestAlgorithm(
         &digest_algorithm));
-    ASSERT_EQ(rtc::DIGEST_SHA_1, digest_algorithm);
+    ASSERT_EQ(rtc::DIGEST_SHA_256, digest_algorithm);
     ASSERT_TRUE(identity2_->certificate().GetSignatureDigestAlgorithm(
         &digest_algorithm));
-    ASSERT_EQ(rtc::DIGEST_SHA_1, digest_algorithm);
+    ASSERT_EQ(rtc::DIGEST_SHA_256, digest_algorithm);
 
     // The test certificate has an MD5-based signature.
     ASSERT_TRUE(test_cert_->GetSignatureDigestAlgorithm(&digest_algorithm));