Implement current/pending session description methods.

BUG=webrtc:6917

Review-Url: https://codereview.webrtc.org/2590753002
Cr-Commit-Position: refs/heads/master@{#15722}
diff --git a/webrtc/api/peerconnection.cc b/webrtc/api/peerconnection.cc
index 6d7d07d..cdf5a97 100644
--- a/webrtc/api/peerconnection.cc
+++ b/webrtc/api/peerconnection.cc
@@ -1381,6 +1381,26 @@
   return session_->remote_description();
 }
 
+const SessionDescriptionInterface* PeerConnection::current_local_description()
+    const {
+  return session_->current_local_description();
+}
+
+const SessionDescriptionInterface* PeerConnection::current_remote_description()
+    const {
+  return session_->current_remote_description();
+}
+
+const SessionDescriptionInterface* PeerConnection::pending_local_description()
+    const {
+  return session_->pending_local_description();
+}
+
+const SessionDescriptionInterface* PeerConnection::pending_remote_description()
+    const {
+  return session_->pending_remote_description();
+}
+
 void PeerConnection::Close() {
   TRACE_EVENT0("webrtc", "PeerConnection::Close");
   // Update stats here so that we have the most recent stats for tracks and