Re-land: Add API to get negotiated SSL ciphers

This CL adds an API to the SSL stream adapters and transport channels to get the SSL cipher that was negotiated with the remote peer.

The previously approved CL https://webrtc-codereview.appspot.com/26009004/ was reverted in https://webrtc-codereview.appspot.com/40689004/ due to compilation issues while rolling into Chromium.
As the new method has landed in Chromium in https://crrev.com/bc321c76ace6e1d5a03440e554ccb207159802ec, this should be safe to land here now.

BUG=3976
R=pthatcher@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/37209004

Cr-Commit-Position: refs/heads/master@{#8343}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8343 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/webrtc/base/sslstreamadapter.cc b/webrtc/base/sslstreamadapter.cc
index 44df2ee..513ae8c 100644
--- a/webrtc/base/sslstreamadapter.cc
+++ b/webrtc/base/sslstreamadapter.cc
@@ -50,6 +50,9 @@
 bool SSLStreamAdapter::HaveDtls() { return false; }
 bool SSLStreamAdapter::HaveDtlsSrtp() { return false; }
 bool SSLStreamAdapter::HaveExporter() { return false; }
+std::string SSLStreamAdapter::GetDefaultSslCipher() {
+  return std::string();
+}
 #elif SSL_USE_OPENSSL
 bool SSLStreamAdapter::HaveDtls() {
   return OpenSSLStreamAdapter::HaveDtls();
@@ -60,6 +63,9 @@
 bool SSLStreamAdapter::HaveExporter() {
   return OpenSSLStreamAdapter::HaveExporter();
 }
+std::string SSLStreamAdapter::GetDefaultSslCipher() {
+  return OpenSSLStreamAdapter::GetDefaultSslCipher();
+}
 #elif SSL_USE_NSS
 bool SSLStreamAdapter::HaveDtls() {
   return NSSStreamAdapter::HaveDtls();
@@ -70,6 +76,9 @@
 bool SSLStreamAdapter::HaveExporter() {
   return NSSStreamAdapter::HaveExporter();
 }
+std::string SSLStreamAdapter::GetDefaultSslCipher() {
+  return NSSStreamAdapter::GetDefaultSslCipher();
+}
 #endif  // !SSL_USE_SCHANNEL && !SSL_USE_OPENSSL && !SSL_USE_NSS
 
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